^BR₂BodPR₂: highly fluorescent alternatives to PPh₃ and PhPCy₂

Abstract

The syntheses of highly fluorescent analogues of PPh₃ and PhPCy₂ based on the Bodipy chromophore are described. The ligands have been incorporated into two- to four-coordinate group 11 metal complexes. The synthesis, characterisation and photophysical properties of the novel ligands and their metal complexes are reported; many of these compounds have also been characterised by single-crystal X-ray diffraction. Incorporation of the phosphino group and complexation to the group 11 metal centre has little effect on the absorption and emission profiles; high molar extinction coefficients and fluorescence quantum yields were still obtained. In particular, incorporation of the dicyclohexylphosphino substituent significantly increases the quantum yields relative to the parent dyes.

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Introduction

Metal complexes of fluorescent phosphines have potential applications in diagnostic cell imaging¹ and catalytic reaction monitoring,² by virtue of the sensitivity of the fluorescence technique. As an imaging tool used in vitro, fluorescence microscopy produces high spatial resolution of the nanometre order, giving accurate images of processes at the subcellular level;^1,3 there is current interest in incorporating fluorescent tags onto radiopharmaceuticals, because it is otherwise difficult to image the localisation of such probes in detail. A fluorescent radiopharmaceutical would instead facilitate both in vivo and in vitro imaging,³ allowing one to gain a better understanding of the probe's mechanism and localisation within cells. The sensitivity of fluorescence spectroscopy compared to its NMR counterpart (10⁻⁶ to 10⁻⁷ M), also signifies that the detection of low concentrations of catalytically active species – undetectable by other means – ought to also be possible.² However, phosphines conjugated to organic fluorophores often suffer from fluorescence quenching⁴ due to reductive photoinduced electron transfer, therefore synthetic routes to this class of compound have not been extensively reported and fluorescent phosphines remain somewhat rare.⁵

F-Bodipy has desirable photophysical properties which include a high fluorescence quantum yield, strong UV-absorption, chemical robustness and good solubility (Fig. 1).⁶ A common site of modification is at the meso position due to its easy synthetic incorporation.⁶ Over the last few years new synthetic procedures have been developed for the substitution of the fluorides with aryl/alkyl (C-Bodipy) or ethynyl (E-Bodipy) groups; this development has allowed more sophisticated functions to be introduced on the Bodipy backbone.⁶ Given the desirable properties of Bodipy and the extensive synthetic routes to derivatives,⁶ we aimed to create fluorescent tertiary phosphines based on this versatile fluorophore, coordinate the new ligands to transition metals and study their behaviour.

Fig. 1 F-Bodipy (I) and auranofin (II).

Group 11 metal phosphine complexes are sought after, in part, due to their known medicinal applications.⁷ Gold(I),⁸ silver(I)⁹ and copper(I)¹⁰ phosphine complexes have all shown cytotoxic activity, with significant anti-tumour properties – current complexes are based on monodentate and bidentate phosphines. One breakthrough was the discovery of auranofin (Fig. 1) in the early 1980s by Sutton,¹¹ a gold(I) phosphine complex, that was approved for clinical use in 1985 to treat rheumatoid arthritis, but which has also been shown to exhibit anticancer properties,¹² and led to the development of several two-coordinate gold(I) phosphine analogues.⁸

To further develop the possibility of using gold-based drugs, a greater knowledge of their subcellular distribution and mechanism of action is desirable – a fluorescent gold phosphine complex could help to understand the biodistribution of such compounds at high resolution and precision.^1,3 Both gold and silver also have potential in therapeutic nuclear medicine due to the beta-emitting radioisotopes ¹⁹⁹Au and ¹¹¹Ag, which have long half-lives of 3.15 and 7.5 days respectively.¹³ Copper has a range of radionuclides, but the most commonly investigated is ⁶⁴Cu – a positron emitter – and thus can be used for diagnostic nuclear medicine purposes in Positron Emission Tomography (PET) imaging; its relatively long half-life of 762 minutes is considered attractive.¹⁴ For the aforementioned reasons it would therefore be interesting to investigate the coordination chemistry of novel fluorescent monodentate phosphines with the group 11 metals and measure the photophysical properties of any complexes so synthesised, to ascertain if they are suitable for study in the applications already discussed above.

Results and discussion

Synthesis of Bodipy monodentate phosphines

Scheme 1 details our synthesis of the four novel Bodipy monodentate tertiary phosphines 2a/2b and 3a/3b, substituted at the meso position; aryl bromides 1a and 1b¹⁵ were lithiated by reacting with n-butyllithium in diethyl ether at −78 °C to room temperature, followed by the addition of chlorodiphenylphosphine or chlorodicyclohexylphosphine. Both aryl- and alkylchlorophosphines reacted in a similar manner and we also found that the substituent at the boron atom had a limited effect on the overall reactivity of the aryl bromide; all four ligands were produced in good yields ranging from 60 to 84%. The route thus depicts a mild synthetic method for preparing phosphines containing a Bodipy fluorophore.

Scheme 1 Synthesis of the C-Bodipy substituted tertiary phosphine derivatives.

The ³¹P{¹H} NMR spectra of the triarylphosphines in d-chloroform showed 2a/2b at δ −5.5 ppm; aryldialkylphosphines 3a and 3b are shifted downfield to δ 2.7 and 2.8 ppm respectively, due to the electron-donating cyclohexyl rings.

Crystals of 2a were analysed by X-ray crystallography and its molecular structure is depicted in Fig. 2; similar atom numbering schemes are used for all the crystal structures. The P–C bond lengths of 1.8302(19), 1.834(2) and 1.827(2) Å and C–P–C bond angles of 104.03(9), 101.66(9) and 102.40(9)° are typical for tertiary phosphines and compare well to triphenylphosphine.¹⁶

Fig. 2 Molecular structure of 2a with 30% probability displacement ellipsoids (as in other figures). Hydrogen atoms have been omitted for clarity. Selected bond distances [Å] and angles [°]: P–C21 1.8302(19), P–C24 1.834(2), P–C30 1.827(2), C4–C5 1.395(3), N1–C4 1.400(2), N1–B 1.568(2), B–C36 1.626(3); C21–P–C24 101.66(9), C21–P–C30 104.03(9), C24–P–C30 102.40(9), C4–C5–C6 122.44(16), B–N1–C4 123.14(15), N1–B–C36 107.65(15), N1–B–N2 105.17(15).

Coordination chemistry

Copper. Tetrakis(acetonitrile)copper(I) hexafluorophosphate was treated with two equivalents of 2a/2b or 3a/3b in dichloromethane which led to the formation of [Cu(2a/2b)₂(CH₃CN)][PF₆] (4a/4b) and [Cu(3a/3b)₂(CH₃CN)][PF₆] (5a/5b), as depicted in Scheme 2; two phosphines coordinate to the copper(I) centre, replacing the labile acetonitrile ligands. Coordination of the phosphines causes a broadening and downfield shift of the ³¹P{¹H} NMR signal from δ −5.5, and 2.7/2.8 ppm for the free phosphines 2a/2b and 3a/3b to δ 0.0/0.1, and 13.4/12.7 ppm for the complexes 4a/4b and 5a/5b respectively – these values compare well to other copper(I) acetonitrile phosphine complexes.^17,18 Crystals of 4a and 4b suitable for X-ray crystallography were obtained by slow diffusion from ethanol/pentane; the molecular structure of 4b is depicted in Fig. 3, whilst the structure of a compound obtained from the attempted recrystallization of 4a is given in the ESI.† Complex 4b contains a three-coordinate copper(I) centre with a non-coordinating PF₆⁻ anion and one ethanol molecule, which has exchanged for the labile acetonitrile ligand, coordinated to the copper centre.

Scheme 2 Synthesis of copper(I) complexes 4a/4b and 5a/5b.

Fig. 3 View of the molecular structure of 4b with selected atom labels. Hydrogen atoms bound to carbon have been omitted for clarity. Selected bond distances [Å] and angles [°]: Cu–P1 2.2384(11), Cu–P2 2.2273(11), Cu–O5 2.063(3), P1–C23 1.824(4), P1–C26 1.821(4), P1–C32 1.831(4), O5–C75 1.409(5); P1–Cu–P2 130.49(4), P1–Cu–O5 113.61(9), P2–Cu–O5 115.43(9).

The Cu–P bond lengths of 2.2384(11) and 2.2273(11) Å are typical for copper(I) complexes.^18,19 The complex has a distorted trigonal planar geometry for copper, shown by the P1–Cu–P2, P1–Cu–O5 and P2–Cu–O5 bond angles of 130.49(4)°, 113.61(9)° and 115.43(9)° respectively; both the phosphorus atoms are slightly tilted towards the ethanol molecule. The anion⋯Cu(I) interaction is weak as signified by the closest Cu⋯F distance of 3.156 Å. The analogous reaction of a 2 : 1 ratio of triphenylphosphine and [Cu(CH₃CN)₄][PF₆] resulted in the distorted four-coordinate tetrahedral complex [Cu(PPh₃)₂(CH₃CN)₂].^17,20 Ligand 2b is sterically more bulky than triphenylphosphine, and therefore the four-coordinate structure may be too crowded for the first-row d¹⁰ transition metal in this case.

Complex 5a was crystallised by slow solvent diffusion (chloroform–diethyl ether); two types of crystals were produced and their molecular structures are shown in Fig. 4. Structure A is a three-coordinate copper(I) complex with two phosphines and one acetonitrile ligand coordinated to the copper centre, and a non-coordinating anion, PF₆⁻. The Cu–P bond lengths of 2.2273(11) and 2.2564(10) Å are typical of copper(I) phosphine complexes.^18,19 The complex has a distorted trigonal planar geometry as shown by the P1–Cu–P2, P1–Cu–N5 and P2–Cu–N5 bond angles of 136.11(4)°, 120.68(10)° and 102.36(10)° respectively; the P1–Cu–P2 angle is larger than in complex 4b due to the steric bulk of the cyclohexyl groups. The anion⋯Cu(I) interaction is again weak, as signified by the closest Cu⋯F distance of 3.228 Å. Structure B is a distorted trigonal-planar copper(I) complex with two phosphines coordinated and no bound acetonitrile ligands, but the PF₆⁻ anion (modelled with disorder) is weakly coordinated to the copper centre as shown by a stronger anion⋯Cu(I) interaction than in structure A; the alternative closest Cu⋯F distances are 2.741(7) Å to F6A as shown in Fig. 4, and 2.964(11) Å to F6B (not shown); F6A is disordered over two symmetry-related positions in the trigonal plane with the copper centre (on a twofold rotation axis) and two P atoms. All other Cu⋯F distances are >4 Å and are thus non-bonded. A search of the Cambridge Structural Database²¹ reveals 11 structures recorded with weakly coordinated PF₆⁻ and BF₄⁻ anions having Cu⋯F > 2.7 Å.²² The P–Cu–P bond angle of 149.98(9)° is large for a three-coordinate structure but is consistent with the steric bulk of the cyclohexyl groups and is similar to that in the three-coordinate complex [Cu(PCy₃)₂(ClO₄)], which has a P–Cu–P angle of 144.46(6)°.²³ The symmetry-equivalent Cu–P bonds lengths of 2.2280(15) Å are typical and compare well with [Cu(PCy₃)₂][PF₆], which was prepared by Che et al.¹⁸ In that complex the crystal structure reveals a two-coordinate linear copper(I) structure, with Cu–P bond lengths of 2.213(1) and 2.313(1) Å, and a much larger P–Cu–P angle of 179.47(3)°, consistent with a linear geometry and ionic PF₆⁻.¹⁸ However, when the counter-ions tetrafluoroborate and perchlorate were employed, three-coordinate structures were obtained (similar to 5a, structure B) with copper–fluorine and copper–oxygen distances of 2.420(6) and 2.220(7) Å and P–Cu–P angles of 159.98(8)° and 144.46(6)° respectively.^23,24 Willet et al. showed that dicyclohexylphenylphosphine (which is the closest analogue to 3a and 3b) produced [Cu(PCy₂Ph)₂][ClO₄] with the perchlorate anion, but with tetrafluoroborate a different copper(I) complex formed, [Cu(PCy₂Ph)₂(F–BF₃)]. Currently the crystal structures are not known to confirm whether the counter-ions have any significant coordinating interaction.²⁵

Fig. 4 View of the molecular structures of 5a structure A (top) and 5a structure B (bottom). Hydrogen atoms have been omitted for clarity. Selected bond distances [Å] and angles [°]: 5a structure A – Cu–P1 2.2273(11), Cu–P2 2.2564(10), Cu–N5 1.994(3), P1–C33 1.829(4), P1–C42 1.841(4), P2–C83 1.845(4), N5–C95 1.128(5), C95–C96 1.466(6); P1–Cu–P2 136.11(4), P1–Cu–N5 120.68(10), P2–Cu–N5 102.36(10), C83–P2–C89 107.56(16), C80–P2–C83 101.98(15), Cu–P2–C83 110.59(12), Cu–P2–C80 122.24(12). 5a structure B – Cu–P1 2.2280(15), P1–C33 1.819(4), P1–C36 1.866(5), P1–C42 1.867(5), Cu⋯F6A 2.741; P1–Cu–P1′ 149.98(9), Cu–P1–C33 121.92(17), Cu–P1–C36 111.55(16), C33–P1–C36 102.6(2).

Silver. Treatment of a dichloromethane solution of (1,5-cyclooctadiene)hexafluoroacetylacetonatosilver(I) ([Ag(η²:η²-cod)(hfa)]) with two equivalents of 2a/2b or 3a/3b led to the formation of the neutral silver(I) complexes [Ag(2a/2b)₂(hfa)] (6a and 6b) and [Ag(3a/3b)₂(hfa)] (7a and 7b), as depicted in Scheme 3. Two phosphines coordinate to the silver, displacing the labile 1,5-cyclooctadiene, to give the products in nearly quantitative yields. Silver has two NMR-active isotopes, ¹⁰⁷Ag (I = 1/2, natural abundance 52%) and ¹⁰⁹Ag (I = 1/2, natural abundance 48%), therefore the expected ³¹P{¹H} NMR spectra for 6a/6b and 7a/7b would consist of two doublets arising from ¹⁰⁷Ag–P and ¹⁰⁹Ag–P spin–spin coupling.²⁶

Scheme 3 Synthesis of the silver(I) complexes 6a/6b and 7a/7b.

Phosphine coordination resulted in a downfield shift of the ³¹P{¹H} NMR signal at room temperature from δ −5.5 ppm for the free phosphines 2a/2b to broad peaks at δ 10.2 and 6.6 ppm for the complexes 6a and 6b respectively (Fig. 5 and ESI†); the signal was a broad singlet at elevated temperatures in both cases, which likely results from rapid phosphine exchange.²⁶ This lability is reduced at low temperatures and the Ag–P coupling can be observed.²⁶

Fig. 5 ³¹P{¹H} VT NMR of [Ag(2b)₂(hfa)] 6b, in d₈-toluene.

At low temperature (−40 °C) two doublets appeared; ¹J_107AgP = 444 Hz and ¹J_109AgP = 511 Hz, and ¹J_107AgP = 446 Hz and ¹J_109AgP = 507 Hz coupling constants were observed for 6a and 6b respectively; these values are typical for silver(I) complexes with two phosphines bound^26,27 and compare well to [Ag(PEt₃)₂(hfa)] (¹J_107AgP = 468 Hz).²⁸ For both 6a and 6b a second set of two low-intensity doublets was observed at −40 °C and indicates that a second silver species was present in solution. For these signals the following Ag–P couplings were measured: ¹J_107AgP = 696 Hz and ¹J_109AgP = 803 Hz, and ¹J_107AgP = 590 Hz and ¹J_109AgP = 677 Hz for 6a and 6b respectively. The increase in Ag–P coupling constants indicates a change in the hybridisation state of the silver(I) complex^26,27 and is attributed to [Ag(2a/2b)(hfa)] with only one phosphine ligand bound. The coupling constants are similar to the reported values for [Ag(PR₃)(hfa)] (R = Ph, Me, Et): ¹J_107AgP = 700–760 Hz.^28,29

Puddephatt et al. reported that an equilibrium is established on the addition of excess phosphine to [Ag(PR₃)(hfa)] complexes and showed that the Ag–hfa bonding is more ionic when extra phosphines are present.^28,30 Mass spectrometry confirmed the [Ag(2a/2b)₂]⁺ product, giving peaks at m/z of 1469.6056 (6a) and 1217.5443 (6b), with loss of the hfa ligand. Low-intensity peaks at 786.2561 and 663.2251 were also observed, which correspond to [Ag(2a/2b)]⁺, in addition to peaks at 2148.9477 and 1777.8560 for the tris-cations [Ag(113a/113b)₃]⁺, but these latter species were not detected by NMR spectroscopy.

On coordination of the dicyclohexyl phosphines 3a and 3b the ³¹P{¹H} NMR signals at room temperature were also shifted downfield for the complexes 7a and 7b; however, instead of a broad singlet, two broadened doublets were observed at δ 23.7 ppm and δ 23.9 ppm for 7a and 7b respectively (Fig. 6 and ESI†). The following Ag–P coupling constants were observed for 7a and 7b respectively: ¹J_107AgP = 453 Hz and ¹J_109AgP = 517 Hz, and ¹J_107AgP = 453 Hz and ¹J_109AgP = 519 Hz. At higher temperatures (120 °C) 7a and 7b gave a broad singlet.

Fig. 6 ³¹P{¹H} VT NMR of [Ag(3b)₂(hfa)] 7b, in d₁₀-o-xylene.

The observation of Ag–P coupling at room temperature was unusual since the rapid exchange of the phosphine ligands usually causes this coupling to be averaged to zero; this ligand exchange is normally slowed down by cooling the solution to low temperatures (as is the case for 6a and 6b).²⁷ However, the observation of Ag–P coupling at room temperature has been reported previously, where the phosphine is sterically hindered or chelating.^27,31 Phosphines 3a and 3b are also bulky which may explain the lower rate of phosphine exchange and the observation of Ag–P coupling. The electrospray mass spectra gave peaks for [M − (hfa)]⁺ at m/z of 1489.7998 for 7a, and 1242.7354 for 7b. Complexes 6a and 7b were also characterised by X-ray crystallography (Fig. 7). The complexes have neutral silver(I) tetrahedral four-coordinate geometries with two phosphines and one hfa ligand bound to the metal. The Ag–P bond lengths of 2.4255(10) Å and 2.4028(13) Å are typical for silver(I) phosphine complexes.^25,30,32 The complexes are somewhat distorted, shown by the P–Ag–P, P–Ag–O and O–Ag–O bond angles (Fig. 7 caption). The synthesis of a related four-coordinate silver(I) complex [Ag(PPh₃)₂(hfa)] has been reported in a similar fashion, but currently no crystal structure is known.³³

Fig. 7 Molecular structures of 6a (top) and 7b (bottom). Hydrogen atoms omitted for clarity. Selected bond distances [Å] and angles [°]: 6a – Ag–P 2.4255(10), Ag–O 2.407(3), P–C33 1.833(4), P–C36 1.824(4), P–C42 1.825(4), O–C48 1.230(5), C48–C49 1.394(6), C48–C50 1.528(7), F1–C50 1.281(6), C4–C5 1.394(5); P–Ag–P′ 135.24(5), P–Ag–O 102.34(8), O–Ag–O′ 76.40(15), Ag–P–C33 119.40(13), Ag–P–C36 114.02(13), Ag–P–C42 110.39(13), C33–P–C36 101.79(17), C36–P–C42 103.39(19), Ag–O–C48 129.9(3), O–C48–C49 129.3(5), O–C48–C50 112.9(4), C49–C48–C50 117.8(5). 7b – Ag–P 2.4028(13), Ag–O1 2.337(6), Ag–O2 2.718(8), P–C21 1.813(5), P–C26 1.826(5), P–C32 1.844(5), O1–C39 1.231(11), O2–C41 1.233(13), C39–C40 1.392(14), C40–C41 1.403(14), F1–C38 1.345(16); P–Ag–P′ 141.99(7), P–Ag–O1 112.2(4), O1–Ag–O2 71.93(3), Ag–P–C21 115.98(17), Ag–P–C26 111.93(18), Ag–P–C32 110.70(17), C21–P–C32 103.8(2), C26–P–C32 108.0(3), Ag–O1–C39 135.9(7), O1–C39–C40 132.0(11), O1–C39–C38 111.9(10), C38–C39–C40 115.7(10). Primes denote symmetry-generated atoms.

However, the three-coordinate complex [Ag(PPh₃)(hfa)] has had its solid state structure determined – shorter bond lengths are observed: 2.346(3) for Ag–P, and 2.341(5) and 2.218(5) Å for Ag–O.²⁹ For 7b the Ag–O bond distances of 2.337(6) Å (Ag–O1) and 2.718(8) Å (Ag–O2) are significantly different, and the latter is longer than the normal covalent silver(I)–oxygen bond length of ca. 2.3 Å, which indicates that the second oxygen is only weakly bonded to the silver;²⁸ the hfa ligand is disordered over two positions related by the twofold rotation axis passing through Ag. The bite angle of the phosphines is larger than in 6a, due to the increased steric bulk of the phosphine 3b. No β-diketonate silver complexes with dicyclohexylphenylphosphine or tricyclohexylphosphine have been reported, however cationic two- and three-coordinate silver(I) complexes do form with dicyclohexylphenylphosphine and the non-coordinating perchlorate, tetrafluoroborate, hexafluorophosphate and hexafluoroantimonate anions.^25,32,33

Gold. Treatment of chloro(tetrahydrothiophene)gold(I) [AuCl(tht)] with one equivalent of 2a/2b or 3a/3b in dichloromethane led to the formation of the neutral gold(I) complexes [AuCl(2a/2b)] (8a and 8b) and [AuCl(3a/3b)] (9a and 9b), as depicted in Scheme 4. In each case one phosphine coordinates to the gold, replacing the labile tht ligand; purification was achieved by column chromatography, resulting in high yields of 75–91%.

Scheme 4 Synthesis of the gold(I) complexes 8a/8b and 9a/9b.

Coordination of the phosphines resulted in a downfield shift of the ³¹P{¹H} NMR signal of the free phosphines 2a/2b and 3a/3b to δ 33.2/33.3 and 51.4/51.6 ppm for the complexes 8a/8b and 9a/9b respectively. Complexes 8a, 9a and 9b were also characterised by X-ray crystallography (Fig. 8 and ESI†). The solid-state structures show them to be gold(I) two-coordinate linear complexes, as expected.

Fig. 8 View of the molecular structure of 8a (top) and 9a (bottom). Hydrogen atoms have been omitted for clarity. Selected bond distances [Å] and angles [°]: 8a – Au–P 2.223(3), Au–Cl1 2.281(3), P–C21 1.816(12), P–C24 1.817(14), P–C30 1.810(13), C4–N1 1.400(16), N1–B 1.566(17), B–C42 1.65(2); P–Au–Cl1 177.24(14), C21–P–C24 108.1(6), C21–P–C30 104.7(6), C24–P–C30 103.1(6), Au–P–C21 110.7(4), Au–P–C24 113.5(5), Au–P–C30 116.0(4). 9a – Au–P 2.2351(13), Au–Cl 2.2875(13), P–C21 1.817(4), P–C36 1.838(5), P–C42 1.845(4), C4–N1 1.390(5), N1–B 1.574(6), B–C24 1.646(7); P–Au–Cl 178.27(5), C21–P–C36 102.2(2), C21–P–C42 104.0(2), C36–P–C42 109.8(2), Au–P–C21 112.53(15), Au–P–C36 113.34(16), Au–P–C42 113.90(17).

The Au–P and Au–Cl bond lengths are typical for gold(I) compounds (Fig. 8 caption).³⁴ The P–Au–Cl bond angles of 177.24(14)°, 178.27(5)° and 177.55(3)° for 8a, 9a and 9b respectively are close to the ideal 180° for a linear complex. The analogous complex to 8a/8b, [AuCl(PPh₃)], prepared from triphenylphosphine and chloroauric acid, has a slightly longer P–Au bond length (2.235(3) Å), and a slightly larger Au–P–Cl bond angle than 8a (179.68(8)°).^34a The analogous dicyclohexylphenylphosphine complex, [AuCl(PCy₂Ph)], made from the ligand and a reaction mixture of tetrachloroauric acid and 2,2′-thiodiethanol, has P–Au and P–Cl bond lengths of 2.234(2) and 2.281(3) Å respectively and an Au–P–Cl bond angle of 178.3(1)°, very similar to 9a/9b.^34b

Optical properties

After the synthesis of several group 11 metal complexes of 2a/2b and 3a/3b, it was important to determine and understand their photophysical properties. Our initial concern was whether the phosphorus donor⁴ or the heavy metals³⁵ themselves would quench the fluorescence of the Bodipy fluorophore, which has been shown to occur for other fluorophores in phosphorus systems. Photophysical data were collected for all ligands and complexes in dry degassed tetrahydrofuran to minimise photobleaching and phosphine oxidation in solution (Table 1).

Table 1 Photophysical data for phosphines 2a/2b, 3a/3b and the group 11 complexes 4a/4b–9a/9b^a

Compound	λ abs (nm)	λ em (nm)	ε (M^−1 cm^−1)	Φ F
a Measured in dry degassed tetrahydrofuran at room temperature. Fluorescence quantum yields were measured with respect to 4,4-difluoro-8-phenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene.^36
2a	517	534	77 000	0.042
4a (Cu)	518	535	133 000	0.038
6a (Ag)	518	535	151 000	0.036
8a (Au)	519	538	76 000	0.034
2b	513	527	92 000	0.29
4b (Cu)	513	528	167 000	0.29
6b (Ag)	513	528	155 000	0.26
8b (Au)	514	529	74 000	0.20
3a	518	533	77 000	0.073
5a (Cu)	518	534	143 000	0.069
7a (Ag)	518	534	141 000	0.070
9a (Au)	519	536	78 000	0.058
3b	512	526	82 000	0.44
5b (Cu)	512	527	171 000	0.42
7b (Ag)	513	527	157 000	0.43
9b (Au)	514	529	85 000	0.39

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The four phosphine ligands 2a/2b and 3a/3b all show a typical Bodipy profile⁶ with absorption maxima at either 517/513 nm or 518/512 nm depending on the groups at the boron centre; changing from diphenyl to dimethyl causes a hypsochromic shift of the absorption maxima (4–6 nm). The lowest energy maximum is assigned to the S₀–S₁ (π–π*) transition for the Bodipy core. All the ligands have typically high molar absorption coefficients, ranging from 77 000 to 92 000 M⁻¹ cm⁻¹.⁶ Secondly, a lower intensity, broader absorption band can be seen between 370 and 385 nm (ε = 3000–10 000 M⁻¹ cm⁻¹), which is attributed to the S₀–S₂ (π–π*) transition of the Bodipy core. There are also low-intensity, high-energy peaks centred between 250–300 nm for the dicyclohexyl derivatives 3a/3b. The absorption spectra for phosphines 2b/3b and their complexes are given in Fig. 9; the corresponding spectra for 2a/3a and their complexes is given in the ESI.†

Fig. 9 Top: absorption spectra of triarylphosphine 2b and its complexes [Cu(2b)₂(CH₃CN)][PF₆] 4b, [Ag(2b)₂(hfa)] 6b and [AuCl(2b)] 8b. Bottom: absorption spectra of aryldialkylphosphine 3b and its complexes [Cu(3b)₂(CH₃CN)][PF₆] 5b, [Ag(3b)₂(hfa)] 7b and [AuCl(3b)] 9b. All measured in dry degassed tetrahydrofuran at room temperature (concentrations range from 3.0 × 10⁻⁶ to 1.1 × 10⁻⁵ M, see ESI†).

Room-temperature fluorescence of the phosphine ligands was readily detected, with maxima of 534/527 nm or 533/526 nm, again depending on the boron substituents (Fig. 10). The Stokes shifts of 14–17 nm are small, which is common for the Bodipy fluorophore, and suggests that only small structural changes occur on excitation.⁶ The fluorescence quantum yields of 2b (0.29) and 3b (0.44) are typically high for Bodipy molecules and compare well to the parent Bodipy 10b (0.35, ESI†), which shows the phosphorus donor does not quench the fluorescence.

Fig. 10 Top: emission spectra of triarylphosphine 2b and its complexes [Cu(2b)₂(CH₃CN)][PF₆] 4b, [Ag(2b)₂(hfa)] 6b and [AuCl(2b)] 8b. Bottom: emission spectra of aryldialkylphosphine 3b and its complexes [Cu(3b)₂(CH₃CN)][PF₆] 5b, [Ag(3b)₂(hfa)] 7b and [AuCl(3b)] 9b. All measured in dry degassed tetrahydrofuran at room temperature, excitation wavelength = 485 nm, concentrations range from 1.9 × 10⁻⁶ to 4.0 × 10⁻⁶ M, see ESI†).

This is unusual and, as with our previously reported Bodipy primary phosphines,¹⁵ contradicts several phosphine examples.⁴ However, it is perhaps to be expected, given that the DFT calculations (see Fig. 11 and ESI†) show there is no phosphorus character in the HOMO, HOMO−1 or HOMO−2 for 2a and 3a, nor in the HOMO or HOMO−1 for 2b and 3b, and that the energy difference between the HOMO and the first phosphorus-containing orbital is 0.9 eV for all the phosphine ligands (Fig. 11 and ESI†). The quantum yield for 3b is, perhaps surprisingly, also higher than that of the parent Bodipy which has no substituents on the meso phenyl ring (3b = 0.44 and 10b = 0.35). More detailed investigations into a Bodipy phosphine series could reveal how the quantum yield is affected by both the electronic and steric nature of the substituents on the phosphorus. Changing the methyl groups at the boron atom for phenyl groups severely quenches the fluorescence (compare 2b: Φ_F = 0.29 to 2a: Φ_F = 0.042), which is consistent with our previous findings.¹⁵ The absorption spectra of the complexes are very similar to those of the uncoordinated ligands (Fig. 9); wavelengths of the low energy transition fall in the range 519–512 nm. The corresponding molar extinction coefficients are large for the copper (4–5) and silver (6–7) complexes (ε = 133 000–171 000 M⁻¹ cm⁻¹), due to the presence of two Bodipy ligands; the monodentate gold complexes (8–9) retain similar values to the free ligands (ε = 74 000–85 000 M⁻¹ cm⁻¹).

Fig. 11 Calculated molecular orbital surfaces of the triarylphosphine 2a (top two rows) and the aryldialkylphosphine 3a (bottom two rows) from LUMO+1 to HOMO−5.

The fluorescence spectra of the complexes 4b–9b are displayed in Fig. 10. On complexation, the fluorescence quantum yields are generally retained, with only a slight decrease observed on descending the group (for instance 2b: Φ_F = 0.29, 8b: Φ_F = 0.20). The gold species (8–9) have the lowest relative quantum yields, likely due to the heavy atom effect. Quenching is less pronounced for the aryldialkylphosphine complexes of 3b compared to those of the triarylphosphine 2b (Table 1, Fig. 10) and all three metal complexes of 3b have higher quantum yields than the parent Bodipy 10b (Φ_F = 0.35). It is noteworthy that Gray et al. reported group 11 complexes which contained separated azadipyrromethene and triphenylphosphine ligands; however, the molar extinction coefficient and fluorescence quantum yields are significantly lower in those cases, 30 000–65 000 M⁻¹ cm⁻¹ and 0.0024–0.0039 respectively.³⁷

Conclusions

The synthesis of fluorescent monodentate triaryl and aryldialkyl tertiary phosphines has been achieved in excellent yields via the lithiation of the Bodipy aryl bromides 1a/1b, and subsequent addition of the relevant chlorophosphine. This route may be transferable to a range of aryl and alkyl chlorophosphines and thus could be an excellent route to a library of new Bodipy tertiary phosphines. The photophysical properties of the phosphines are intriguing; the fluorescence is not quenched significantly compared to their precursor and, in fact, in the case of aryldialkylphosphines 3a and 3b, the emission is enhanced in comparison to their parent Bodipys 10a and 10b (see ESI†). The novel phosphines 2a/2b and 3a/3b readily coordinate to low-oxidation-state coinage metals at room temperature in nearly quantitative yield; upon coordination, the fluorescence of the phosphines is not significantly quenched. These novel ligands and their complexes have potential applications in medicinal imaging, as the fluorescent Bodipy functionality will facilitate cell imaging. Several group 11 metal phosphine complexes have shown cytotoxic properties against several cancer cell lines,^8–10 and our novel derivatives may well display similar attributes. Future work will focus on their use in diagnostic imaging and therapy.

Experimental

All air- and/or water-sensitive reactions were performed under a nitrogen atmosphere using standard Schlenk line techniques. Tetrahydrofuran and diethyl ether were dried over sodium/benzophenone. Dichloromethane and chloroform were dried over calcium hydride; all solvents were distilled prior to use. Hexane and pentane were purchased in an anhydrous state. Most starting materials were purchased from Aldrich, Acros Organics, Alfa Aesar or Strem and used as received. 4,4-Difluoro-8-phenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene,³⁶ the arylbromides 1a/1b¹⁵ and [AuCl(tht)]³⁸ were prepared according to literature procedures.

Flash chromatography was performed on silica gel from Fluorochem (silica gel, 40–63 μ, 60 Å, LC301). Thin-layer chromatography was performed on Fisher aluminium-based plates with silica gel and fluorescent indicator (254 nm). Infrared spectra were recorded on a Varian 800 FT-IR spectrometer and mass spectrometry was carried out by the EPSRC National Mass Spectrometry Service Centre, Swansea. ¹H, ¹³C{¹H}, ³¹P{¹H}, ¹⁹F{¹H} and ¹¹B{¹H} NMR spectra were recorded on a JEOL Lambda 500 (¹H 500.16 MHz) or JEOL ECS-400 (¹H 399.78 MHz) spectrometer at room temperature (21 °C) using the indicated solvent as internal reference, unless specified otherwise; ¹H and ¹³C shifts were relative to tetramethylsilane, ³¹P relative to 80% H₃PO₄, ¹¹B relative to BF₃·Et₂O and ¹⁹F relative to CFCl₃. It is worth noting that, as for dicyclohexylphenylphosphine,³⁹ six unique cyclohexyl carbon signals are seen in the ¹³C{¹H} NMR spectra for phosphines 3a and 3b and their respective complexes. The six signals arise as the two cyclohexyl rings are equivalent but the carbon atoms that are symmetrically equivalent are diastereotopic; these diastereotopic carbon atoms are also non-equivalent with respect to P–C coupling constants.

All calculations were carried out using Spartan 10 software.⁴⁰ Full geometry optimizations of the studied compounds were performed using density functional theory with a B3LYP/6-31G* basis set. A vibrational analysis was performed at the same level to characterize calculated structures as minima.

Absorption spectra were recorded with a Hitachi Model U-3310 spectrophotometer while fluorescence studies were recorded with a Hitachi F-4500 fluorescence spectrophotometer. Solvents used for spectroscopic experiments were spectrophotometric grade. Absorption and emission spectra were recorded in dry degassed tetrahydrofuran solution at room temperature. Fluorescence quantum yields were measured with respect to 4,4-difluoro-8-phenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (Φ_F = 0.76, λ_abs = 524 nm, λ_em = 537 nm, ε = 86 000 M⁻¹ cm⁻¹, tetrahydrofuran).³⁶ Dyes were excited at 485 nm and excitation slits set to 5 nm.

8-((4-Diphenylphosphino)phenyl)-4,4-diphenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (2a)

8-(4-Bromophenyl)-4,4-diphenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (0.50 g, 0.87 mmol) was dissolved in anhydrous diethyl ether (40 mL) and cooled to −78 °C. n-BuLi (0.38 mL, 0.96 mmol, 2.5 M in hexane) was added dropwise over five minutes and the reaction was warmed to room temperature over 45 min. The solution was cooled back to −78 °C and chlorodiphenylphosphine (0.17 mL, 0.96 mmol) was added dropwise. The reaction mixture was allowed to warm up to room temperature and was stirred for a further two hours. It was washed with water and extracted with diethyl ether (3 × 30 mL). The combined organic fractions were washed with brine (30 mL) and dried over magnesium sulfate. The solvent was removed in vacuo to yield a red/orange solid. The compound was purified using column chromatography on silica gel (toluene–hexane 2 : 3, R_f = 0.4) and gave an orange solid (0.50 g, 84%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–pentane. ¹H NMR (400 MHz, CDCl₃) δ 7.45–7.41 (m, 7H), 7.40–7.35 (m, 11H), 7.29–7.24 (m, 4H), 7.22–7.19 (m, 2H), 2.26 (q, ³J_HH = 7.3 Hz, 4H), 1.82 (s, 6H), 1.44 (s, 6H), 0.94 (t, ³J_HH = 7.3 Hz, 6H) ppm; ¹³C{¹H} NMR (100 MHz, CDCl₃) δ 153.0, 150.8 (br), 140.0, 137.9 (d, J_CP = 11.5 Hz), 137.3, 136.7 (d, J_CP = 10.5 Hz), 135.0, 133.8, 133.6, 133.4, 132.8, 130.6, 129.0, 128.9, 128.6 (d, J_CP = 6.7 Hz), 127.1, 125.4, 17.3, 14.7, 14.5, 12.1 ppm; ³¹P{¹H} NMR (162 MHz, CDCl₃) δ −5.5 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.0 ppm; IR (neat): [small nu, Greek, tilde] = 2958 (w), 1542 (s), 1472 (s), 1396 (s), 1308 (m), 1170 (m), 1143 (m), 1061 (m), 971 (s), 775 (s) cm⁻¹; HRMS (ESI⁺) exact mass calcd for C₄₇H₄₇N₂B₁P₁ [M + H]⁺ requires m/z 681.3544, found m/z 681.3570 (2.6 ppm).

8-((4-Diphenylphosphino)phenyl)-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (2b)

Prepared in the same manner as for 2a using 0.50 g (1.11 mmol) of 8-(4-bromophenyl)-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene, 0.49 mL (1.22 mmol) of n-BuLi (2.5 M in hexane) and 0.22 mL (1.22 mmol) of chlorodicyclohexylphosphine. The compound was purified using column chromatography on silica gel (chloroform–hexane 1 : 5, R_f = 0.3) to yield an orange solid (0.37 g, 60%). ¹H NMR (400 MHz, CDCl₃) δ 7.45–7.42 (m, 2H), 7.41–7.35 (m, 10H), 7.34–7.30 (m, 2H), 2.47 (s, 6H), 2.35 (q, ³J_HH = 7.3 Hz, 4H), 1.36 (s, 6H), 1.01 (t, ³J_HH = 7.3 Hz, 6H), 0.30 (s, 6H) ppm; ¹³C{¹H} NMR (100 MHz, CDCl₃) δ 150.6, 139.8, 137.9, 137.8, 136.7 (d, J_CP = 11.5 Hz), 133.8, 133.6, 133.5, 132.4, 132.1, 132.0, 128.8, 128.5 (d, J_CP = 6.7 Hz), 17.4, 14.7, 14.5, 11.9, 10.4 (br) ppm; ³¹P{¹H} NMR (162 MHz, CDCl₃) δ −5.5 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.9 ppm; IR (neat): [small nu, Greek, tilde] = 2924 (w), 2863 (w), 1552 (s), 1455 (m), 1372 (w), 1314 (s), 1170 (s), 1144 (s), 1064 (m), 977 (s) cm⁻¹; HRMS (EI⁺) exact mass calcd for C₃₇H₄₃N₂B₁P₁ [M + H]⁺ requires m/z 556.3288, found m/z 556.3294 (1.1 ppm).

8-((4-Dicyclohexylphosphino)phenyl)-4,4-diphenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3a)

Prepared in the same manner as for 2a using 0.50 g (0.87 mmol) of 8-(4-bromophenyl)-4,4-diphenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene, 0.38 mL (0.96 mmol) of n-BuLi (2.5 M in hexane) and 0.21 mL (0.96 mmol) of chlorodicyclohexylphosphine. The compound was purified using column chromatography on silica gel (dichloromethane–hexane 1 : 4, R_f = 0.3) to yield an orange solid (0.42 g, 69%). ¹H NMR (500 MHz, CDCl₃) δ 7.59–7.56 (m, 2H), 7.41–7.33 (m, 6H), 7.23–7.17 (m, 6H), 2.22 (q, ³J_HH = 7.8 Hz, 4H), 1.99–1.66 (m, 12H), 1.77 (s, 6H), 1.36–1.02 (m, 10H), 1.33 (s, 6H), 0.90 (t, ³J_HH = 7.8 Hz, 6H) ppm, ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 153.1, 150.8 (br), 140.5, 137.6, 135.2, 135.1, 135.0, 134.0, 133.0, 130.8, 128.4 (d, J_CP = 7.6 Hz), 127.2, 125.6, 32.2 (d, ¹J_CP = 11.5 Hz), 30.1 (d, ²J_CP = 16.3 Hz), 28.7 (d, ²J_CP = 6.7 Hz), 27.3 (d, ³J_CP = 12.5 Hz), 27.1 (d, ³J_CP = 7.7 Hz), 26.7, 17.5, 14.8, 14.7, 12.1 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 2.7 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −0.7 ppm; IR (neat): [small nu, Greek, tilde] = 2925 (m), 2850 (m), 1548 (s), 1474 (m), 1384 (m), 1307 (s), 1168 (s), 1110 (m), 973 (s) cm⁻¹; HRMS (AP⁺) calcd for C₄₇H₅₉B₁N₂P₁ [M + H]⁺ requires m/z 692.4540, found m/z 692.4560 (2.9 ppm).

8-((4-Dicyclohexylphosphino)phenyl)-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (3b)

Prepared in the same manner as for 2a using 0.50 g (1.11 mmol) of 8-(4-bromophenyl)-4,4-dimethyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene, 0.49 mL (1.22 mmol) of n-BuLi (2.5 M in hexane) and 0.27 mL (1.22 mmol) of chlorodicyclohexylphosphine. The compound was purified using column chromatography on silica gel (chloroform–hexane 1 : 4, R_f = 0.4) to yield an orange solid (0.39 g, 62%). ¹H NMR (400 MHz, CDCl₃) δ 7.47 (m, 2H), 7.21 (d, ³J_HH = 8.2 Hz, 2H), 2.37 (s, 6H), 2.23 (q, ³J_HH = 7.3 Hz, 4H), 1.90–1.56 (m, 12H), 1.90 (s, 6H), 1.30–0.78 (m, 10H), 0.90 (t, ³J_HH = 7.3 Hz, 6H), 0.21 (s, 6H) ppm; ¹³C{¹H} NMR (100 MHz, CDCl₃) δ 150.6, 140.2, 137.9, 135.0 (d, J_CP = 19.2 Hz), 134.7 (d, J_CP = 19.2 Hz), 133.8, 132.5, 129.1, 128.3 (d, J_CP = 7.7 Hz), 32.1 (d, ¹J_CP = 12.5 Hz), 29.9 (d, ²J_CP = 16.3 Hz), 28.7 (d, ²J_CP = 6.7 Hz), 27.4 (d, ³J_CP = 12.5 Hz), 27.1 (d, ³J_CP = 6.7 Hz), 26.7, 17.6, 14.8, 14.4, 11.9, 10.5 (br) ppm; ³¹P{¹H} NMR (162 MHz, CDCl₃) δ 2.8 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −2.1 ppm; IR (neat): [small nu, Greek, tilde] = 2927 (w), 2856 (w), 1551 (s), 1448 (m), 1321 (m), 1171 (s), 1145 (s), 946 (s) cm⁻¹; HRMS (AP⁺) calcd for C₃₇H₅₅B₁N₂P₁ [M + H]⁺ requires m/z 568.4227, found m/z 568.4226 (0.1 ppm).

[Cu(2a)₂(CH₃CN)][PF₆] (4a)

Tetrakis(acetonitrile)copper(I)hexafluorophosphate (0.027 g, 0.073 mmol) and 8-(4-diphenylphosphine)phenyl)-4,4-diphenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (0.100 g, 0.147 mmol) were added together to anhydrous dichloromethane (3 mL) and stirred under nitrogen for two hours. After removal of solvent an orange solid was produced (0.107 g, 93%). A sample suitable for X-ray crystallographic analysis was obtained from ethanol–pentane. ¹H NMR (500 MHz, CDCl₃) δ 7.51–7.47 (m, 4H), 7.46–7.40 (m, 12H), 7.39–7.32 (m, 20H), 7.28–7.22 (pseudo t, 8H), 7.21–7.16 (m, 4H), 2.20 (q, ³J_HH = 7.3 Hz, 8H), 2.19 (s, 3H), 1.77 (s, 12H), 1.34 (s, 12H), 0.88 (t, ³J_HH = 7.3 Hz, 12H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 153.7, 150.3 (br), 139.3, 138.9, 134.6, 134.0, 133.9, 133.5, 133.4, 131.8, 131.0, 130.8, 130.5, 130.0, 129.4, 127.3, 125.7, 120.3, 17.7, 14.8, 14.7, 12.3, 2.31 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 0.0 (br), −143.6 (septet, ¹J_PF = 712.6 Hz) ppm; ¹¹B{¹H} NMR (162 MHz, CDCl₃) δ −1.0 ppm; IR (neat): [small nu, Greek, tilde] = 2960 (w), 2925 (w), 2869 (w), 1548 (s), 1473 (m), 1435 (m), 1397 (m), 1362 (m), 1305 (m), 1263 (w), 1173 (s), 1144 (m), 974 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₉₄H₉₂B₂N₄P₂Cu₁ [M − C₂H₃N₁]⁺ requires m/z 1421.6346, found m/z 1421.6335 (0.8 ppm).

[Cu(2b)₂(CH₃CN)][PF₆] (4b)

Prepared in the same manner as for 4a using 0.034 g (0.090 mmol) of tetrakis(acetonitrile)copper(I) hexafluorophosphate and 0.100 g (0.180 mmol) of 2b. Yield 0.115 g (97%). A sample suitable for X-ray crystallographic analysis was obtained from ethanol–pentane. ¹H NMR (500 MHz, CDCl₃) δ 7.48 (m, 5H), 7.39 (m, 12H), 7.30 (m, 11H), 2.46 (s, 12H), 2.28 (q, ³J_HH = 7.3 Hz, 8H), 2.14 (s, 3H), 1.26 (s, 12H), 0.96 (t, ³J_HH = 7.3 Hz, 12H), 0.28 (s, 12H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 151.2, 140.4, 138.6, 134.1, 133.5, 133.1, 133.0, 131.6, 130.9, 130.8, 129.9, 129.4, 128.7, 120.6, 17.5, 14.8, 14.4, 12.1, 10.5 (br), 2.2 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 0.1 (br), −143.6 (septet, ¹J_PF = 712.6 Hz) ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.8 ppm; IR (neat): [small nu, Greek, tilde] = 2959 (w), 2925 (w), 2869 (w), 1551 (s), 1471 (m), 1435 (m), 1360 (m), 1320 (s), 1264 (w), 1173 (s), 1145 (s), 1112 (m), 1026 (w), 981 (m), 945 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₇₄H₈₄B₂N₄P₂Cu₁ [M − C₂H₃N₁]⁺ requires m/z 1173.5720, found m/z 1173.5927 (0.9 ppm).

[Cu(3a)₂(CH₃CN)][PF₆] (5a)

Prepared in the same manner as for 4a using 0.027 g (0.072 mmol) of tetrakis(acetonitrile)copper(I) hexafluorophosphate and 0.100 g (0.144 mmol) of 3a. Yield 0.114 g (97%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–pentane. ¹H NMR (500 MHz, CDCl₃) δ 7.67 (m, 4H), 7.48–7.34 (m, 12H), 7.25–7.18 (m, 12H), 2.42–2.23 (m, 4H), 2.22 (br, 3H), 2.13 (q, ³J_HH = 7.3 Hz, 8H), 1.91–1.61 (m, 16H), 1.76 (s, 12H), 1.47–1.06 (m, 24H), 1.36 (s, 12H), 0.83 (t, ³J_HH = 7.3 Hz, 12H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 153.8, 150.2 (br), 140.4, 138.7, 134.9 (m), 134.4, 133.9, 133.4, 130.4, 129.7 (m), 127.3, 126.8 (pseudo t, J_CP = 15.1 Hz), 125.7, 121.9, 31.8 (pseudo t, ¹J_CP = 10.6 Hz), 29.7 (br), 28.6, 26.8 (pseudo t, ³J_CP = 6.8 Hz), 26.6 (pseudo t, ³J_CP = 4.8 Hz), 26.2, 17.4, 14.8, 14.7, 12.2, 2.5 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 13.4 (br), −143.5 (septet, ¹J_PF = 712.6 Hz) ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −0.2 ppm; IR (neat): [small nu, Greek, tilde] = 2960 (w), 2929 (w), 2854 (w), 1549 (s), 1475 (m), 1449 (w), 1397 (w), 1362 (w), 1304 (m), 1263 (w), 1173 (s), 1145 (m), 1112 (m), 974 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₉₄H₁₁₆B₂N₄P₂Cu₁ [M − C₂H₃N₁]⁺ requires m/z 1445.8224, found m/z 1445.8197 (1.9 ppm).

[Cu(3b)₂(CH₃CN)][PF₆] (5b)

Prepared in the same manner as for 4a using 0.033 g (0.088 mmol) of tetrakis(acetonitrile)copper(I) hexafluorophosphate and 0.100 g (0.176 mmol) of 3b. Yield 0.117 g (96%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–pentane. ¹H NMR (500 MHz, CDCl₃) δ 7.61 (m, 4H), 7.38 (d, ³J_HH = 7.3 Hz, 4H), 2.43 (s, 12H), 2.34 (m, 3H), 2.20 (q, ³J_HH = 7.3 Hz, 8H), 2.21 (m, 4H), 1.90 (m, 4H), 1.75 (12H), 1.44–1.03 (m, 24H), 1.18 (s, 12H), 0.94 (t, ³J_HH = 7.3 Hz, 12H), 0.26 (s, 12H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 151.2, 140.7, 138.4, 134.9, 133.0, 132.9, 129.4, 128.6, 126.6 (pseudo t, J_CP = 15.2 Hz), 122.5, 31.8 (pseudo t, ¹J_CP = 10.6 Hz), 29.7 (br), 28.6, 26.8 (pseudo t, ³J_CP = 5.8 Hz), 26.6 (pseudo t, ³J_CP = 5.1 Hz), 26.2, 17.4, 14.7, 14.4, 11.9, 10.4 (br), 2.5 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 12.7 (br), −143.6 (septet, ¹J_PF = 712.6 Hz) ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.7 ppm; IR (neat): [small nu, Greek, tilde] = 2959 (w), 2929 (w), 2854 (w), 1552 (s), 1448 (m), 1360 (m), 1320 (s), 1261 (m), 1173 (s), 1146 (s), 1112 (m), 1021 (w), 982 (m), 945 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₇₄H₁₀₈B₂N₄P₂Cu₁ [M − C₂H₃N₁]⁺ requires m/z 1197.7598, found m/z 1197.7583 (1.3 ppm).

[Ag(2a)₂(hfa)] (6a)

(1,5-Cyclooctadiene)(hexafluoroacetylacetonato)silver(I) (0.031 g, 0.074 mmol), and 8-(4-diphenylphosphine)phenyl)-4,4-diphenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (0.100 g, 0.147 mmol) were added together to anhydrous dichloromethane (2 mL) in a darkened flask and stirred at room temperature under nitrogen for one hour. After removal of the solvent an orange solid was produced, which was washed with anhydrous hexane (3 × 5 mL). Yield 0.103 g (87%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–hexane. ¹H NMR (500 MHz, CDCl₃) δ 7.63–7.55 (br d, ³J_HH = 7.6 Hz, 4H), 7.52–7.45 (m, 12H), 7.43–7.37 (m, 20H), 7.29–7.24 (m, 8H), 7.23–7.18 (m, 4H), 5.70 (br, 1H), 2.40 (q, ³J_HH = 7.8 Hz, 8H), 1.80 (s, 12H), 1.35 (s, 12H), 0.91 (t, ³J_HH = 7.8 Hz, 12H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 175.9 (d, J_CP = 30.7 Hz), 153.6, 150.5 (br), 139.9 (d, J_CP = 37.4 Hz), 134.9, 134.4 (d, J_CP = 6.7 Hz), 134.2, 133.9, 133.2, 132.8, 131.8, 131.6, 130.6, 130.5, 129.7, 129.1, 127.3, 125.6, 117.9 (q, ¹J_CF = 288.9 Hz), 86.7, 17.5, 14.8, 14.7, 12.2 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 10.2 (br) ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.1 ppm; ¹⁹F{¹H} NMR (376 MHz, CDCl₃) δ −76.6 ppm; IR (neat): [small nu, Greek, tilde] = 2966 (w), 2928 (w), 2870 (w), 1662 (m), 1520 (s), 1472 (m), 1434 (m), 1302 (m), 1171 (s), 972 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₉₄H₉₂B₂N₄P₂Ag₁ [M − (C₅H₁F₆O₂)]⁺ requires m/z 1469.6068, found m/z 1469.6056 (1.6 ppm).

[Ag(2b)₂(hfa)] (6b)

Prepared as for 6a using 0.038 g (0.090 mmol) of (1,5-cyclooctadiene)(hexafluoroacetylacetonato)silver(I) and 0.100 g (0.180 mmol) of 2b. Yield 0.103 g (80%). ¹H NMR (400 MHz, CDCl₃) δ 7.44–7.23 (m, 28H), 5.90 (br, 1H), 2.44 (s, 12H), 2.29 (q, ³J_HH = 7.3 Hz, 8H), 1.24 (s, 12H), 0.96 (t, ³J_HH = 7.3 Hz, 12H), 0.27 (s, 12H) ppm; ¹³C{¹H} NMR (100 MHz, CDCl₃) δ 175.8 (d, J_CP = 30.8 Hz), 151.0, 139.6, 138.9, 134.2 (d, J_CP = 17.3 Hz), 133.7 (d, J_CP = 17.3 Hz), 133.3, 133.1, 132.7, 132.3 (d, J_CP = 23.0 Hz), 130.3, 129.5 (d, J_CP = 9.6 Hz), 129.0 (d, J_CP = 8.6 Hz), 128.7, 117.9 (q, ¹J_CF = 290.4 Hz), 88.9, 17.4, 14.6, 14.3, 11.9, 10.4 (br) ppm; ³¹P{¹H} NMR (162 MHz, CDCl₃) δ 6.6 (br) ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −2.2 ppm; ¹⁹F{¹H} NMR (376 MHz, CDCl₃) δ −76.5 ppm; IR (neat): [small nu, Greek, tilde] = 2963 (w), 2932 (w), 2871 (w), 1660 (m), 1552 (s), 1538 (s), 1436 (m), 1321 (s), 1253 (s), 1172 (s), 1143 (s), 945 (s), 800 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₇₄H₈₄B₂N₄P₂Ag₁ [M − (C₅H₁F₆O₂)]⁺ requires m/z 1217.5475, found m/z 1217.5443 (2.5 ppm).

[Ag(3a)₂(hfa)] (7a)

Prepared as for 6a using 0.031 g (0.072 mmol) of (1,5-cyclooctadiene)(hexafluoroacetylacetonato)silver(I) and 0.100 g (0.144 mmol) of 3a. Yield 0.110 g (90%). ¹H NMR (500 MHz, CDCl₃) δ 7.80–7.90 (m, 4H), 7.42–7.38 (m, 12H), 7.25–7.17 (m, 12H), 5.71 (br, 1H), 2.37–2.01 (m, 8H), 2.19 (q, ³J_HH = 7.3 Hz, 8H), 1.89–1.64 (m, 16H), 1.77 (s, 12H), 1.36–1.06 (m, 20H), 1.28 (s, 12H), 0.86 (t, ³J_HH = 7.3 Hz, 12H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 175.0 (d, J_CP = 30.2 Hz), 153.5, 150.4 (br), 139.5 (d, J_CP = 8.6 Hz), 135.4, 134.9, 133.9, 133.7, 133.2, 130.5, 129.1, 127.3, 125.6, 125.2, 118.2 (q, ¹J_CF = 290.8 Hz), 85.3, 32.6 (br), 29.4 (br), 28.2, 26.9 (br), 26.8 (br), 26.2, 17.4, 14.8, 14.7, 12.0 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 23.7 (d, ¹J_107AgP = 453 Hz), 23.7 (d, ¹J_109AgP = 517 Hz) ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.0 ppm; ¹⁹F{¹H} NMR (376 MHz, CDCl₃) δ −76.7 ppm; IR (neat): [small nu, Greek, tilde] = 2928 (w), 2853 (w), 1661 (s), 1548 (s), 1522 (s), 1474 (m), 1303 (m), 1250 (m), 1172 (s), 1133 (s), 973 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₉₄H₁₁₆B₂N₄P₂Ag₁ [M − (C₅H₁F₆O₂)]⁺ requires m/z 1489.7979, found m/z 1489.7998 (1.3 ppm).

[Ag(3b)₂(hfa)] (7b)

Prepared as for 6a using 0.037 g (0.090 mmol) of (1,5-cyclooctadiene)(hexafluoroacetylacetonato)silver(I) and 0.100 g (0.176 mmol) of 3b. Yield 0.115 g (90%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–hexane. ¹H NMR (500 MHz, CDCl₃) δ 7.77 (m, 4H), 7.37 (d, ³J_HH = 7.8 Hz, 4H), 5.69 (br, 1H), 2.46 (s, 12H), 2.27 (q, ³J_HH = 7.3 Hz, 8H), 2.22–1.69 (m, 20H), 1.34–0.88 (m, 24H), 1.22 (s, 12H), 0.96 (t, ³J_HH = 7.3 Hz, 12H), 0.29 (s, 12H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 174.9 (d, J_CP = 29.7 Hz), 150.9, 139.8, 139.2, 135.3, 134.5, 133.4, 132.8, 129.0, 128.2, 118.2 (q, ¹J_CF = 290.8 Hz), 85.2, 32.5 (br), 29.3 (br), 28.2, 27.0 (br), 26.9 (br), 26.2, 17.5, 14.7, 14.4, 11.7, 10.5 (br) ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 23.9 (d, ¹J_107AgP = 453 Hz), 23.9 (d, ¹J_109AgP = 519 Hz) ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.8 ppm; ¹⁹F{¹H} NMR (376 MHz, CDCl₃) δ −76.6 ppm; IR (neat): [small nu, Greek, tilde] = 2930 (m), 2857 (w), 1663 (m), 1545 (s), 1525 (m), 1448 (m), 1361 (m), 1321 (s), 1251 (m), 1173 (s), 1146 (s), 944 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₇₄H₁₀₈B₂N₄P₂Ag₁ [M − (C₅H₁F₆O₂)]⁺ requires m/z 1242.7329, found m/z 1242.7354 (2.0 ppm).

[AuCl(2a)] (8a)

Chloro(tetrahydrothiophene)gold(I) (0.047 g, 0.147 mmol) and 8-(4-diphenylphosphine)phenyl)-4,4-diphenyl-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (0.100 g, 0.147 mmol) were added together to anhydrous dichloromethane (2 mL) and stirred under nitrogen for 1 hour. After removal of the solvent an orange/red solid was produced, which was washed with anhydrous hexane (3 × 5 mL) to remove the tetrahydrothiophene. The complex was purified using column chromatography on silica gel (chloroform–hexane 1 : 1, R_f = 0.4) to yield an orange solid (0.101 g, 75%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–hexane. ¹H NMR (400 MHz, CDCl₃) δ 7.68–7.61 (m, 2H), 7.60–7.45 (m, 12H), 7.30–7.28 (m, 4H), 7.18–7.10 (m, 6H), 2.16 (q, ³J_HH = 7.3 Hz, 4H), 1.69 (s, 6H), 1.26 (s, 6H), 0.82 (t, ³J_HH = 7.3 Hz, 6H) ppm; ¹³C{¹H} NMR (100 MHz, CDCl₃) δ 153.7, 149.9 (br), 141.7, 138.2, 134.5, 134.3 (d, J_CP = 13.4 Hz), 134.0 (d, J_CP = 13.4 Hz), 133.7, 133.3, 132.1 (d, J_CP = 2.9 Hz), 130.2, 130.0 (d, J_CP = 11.5 Hz), 129.3 (d, J_CP = 11.5 Hz), 128.6, 127.9, 127.1, 125.5, 17.3, 14.7, 14.6, 12.2 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 33.2 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.1 ppm; IR (neat): [small nu, Greek, tilde] = 2962 (w), 1544 (s), 1472 (m), 1435 (s), 1142 (m), 1101 (m), 972 (s) cm⁻¹; HRMS (ESI⁺) calcd for C₄₇H₄₆B₁N₂P₁Cl₁Au₁ [M]⁺ requires m/z 912.2960, found m/z 911.2989 (3.2 ppm).

[AuCl(2b)] (8b)

Prepared in the same manner as for 8a using 0.058 g (0.180 mmol) of chloro(tetrahydrothiophene)gold(I) and 0.100 g (0.180 mmol) of 2b. The complex was purified using column chromatography on silica gel (dichloromethane–hexane 2 : 1, R_f = 0.4). Yield 0.129 g (91%). ¹H NMR (400 MHz, CDCl₃) δ 7.66–7.58 (m, 2H), 7.57–7.52 (m, 4H), 7.52–7.44 (m, 8H), 2.44 (s, 6H), 2.30 (q, ³J_HH = 7.3 Hz, 4H), 1.28 (s, 6H), 0.99 (t, ³J_HH = 7.3 Hz, 6H), 0.27 (s, 6H) ppm; ¹³C{¹H} NMR (100 MHz, CDCl₃) δ 151.2, 141.6, 137.9, 134.3 (d, J_CP = 13.4 Hz), 134.0 (d, J_CP = 13.4 Hz), 133.1, 132.9, 132.1 (d, J_CP = 1.9 Hz), 129.9 (d, J_CP = 12.4 Hz), 129.3 (d, J_CP = 11.5 Hz), 128.6, 128.5, 128.0, 17.4, 14.6, 14.3, 12.0, 10.3 (br) ppm; ³¹P{¹H} NMR (162 MHz, CDCl₃) δ 33.3 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −2.0 ppm; IR (neat): [small nu, Greek, tilde] = 2962 (w), 2926 (w), 2866 (w), 1552 (s), 1436 (m), 1314 (m), 1170 (s), 1101(s), 946 (s) cm⁻¹; HRMS (AP⁺) calcd for C₃₇H₄₃B₁N₂P₁Cl₁Au₁ [M + H]⁺ requires m/z 788.2642, found m/z 788.2627 (1.9 ppm).

[AuCl(3a)] (9a)

Prepared in the same manner as for 8a using 0.046 g (0.144 mmol) of chloro(tetrahydrothiophene)gold(I) and 0.100 g (0.144 mmol) of 3a. The complex was purified using column chromatography on silica gel (dichloromethane–hexane 1 : 1, R_f = 0.5). Yield 0.116 g (87%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–diethyl ether. ¹H NMR (500 MHz, CDCl₃) δ 7.89–7.78 (m, 2H), 7.52–7.49 (m, 2H), 7.37–7.30 (m, 4H), 7.25–7.16 (m, 6H), 2.32 (m, 2H), 2.21 (q, ³J_HH = 7.3 Hz, 4H), 2.11–2.09 (m, 2H), 1.89–1.63 (m, 8H), 1.77 (s, 6H), 1.43–1.10 (m, 10H), 1.27 (s, 6H), 0.89 (t, ³J_HH = 7.3 Hz, 6H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 153.9, 150.3 (br), 141.3 (d, J_CP = 2.9 Hz), 138.5, 135.3 (d, J_CP = 11.6 Hz), 134.7, 133.9, 133.5, 130.4, 129.7 (d, J_CP = 10.6 Hz), 127.3, 125.7, 125.2, 33.5 (d, ¹J_CP = 34.7 Hz), 29.7 (d, ²J_CP = 1.9 Hz), 28.4, 26.5 (d, ³J_CP = 5.7 Hz), 26.4 (d, ³J_CP = 2.9 Hz), 25.9, 17.4, 14.8, 14.7, 12.2 ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 51.4 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −1.0 ppm; IR (neat): [small nu, Greek, tilde] = 2926 (w), 2854 (w), 1545 (s), 1473 (m), 1304 (m), 1263 (m), 1172 (s), 1143 (m), 972 (s) cm⁻¹; HRMS (AP⁺) calcd for C₄₇H₅₉B₁N₂P₁Au₁Cl₁ [M + H]⁺ requires m/z 924.3897, found m/z 924.3904 (1.1 ppm).

[AuCl(3b)] (9b)

Prepared in the same manner as for 8a using 0.056 g (0.176 mmol) of chloro(tetrahydrothiophene)gold(I) and 0.100 g (0.176 mmol) of 3b. The complex was purified using column chromatography on silica gel (dichloromethane–hexane 1 : 1, R_f = 0.4). Yield 0.121 g (86%). A sample suitable for X-ray crystallographic analysis was obtained from chloroform–pentane. ¹H NMR (500 MHz, CDCl₃) δ 7.78 (m, 2H), 7.47 (m, 2H), 2.44 (s, 6H), 2.30 (q, ³J_HH = 7.5 Hz, 4H), 2.09–1.70 (m, 10H), 1.39–0.85 (m, 12H), 1.21 (s, 6H), 0.98 (t, ³J_HH = 7.5 Hz, 6H), 0.27 (s, 6H) ppm; ¹³C{¹H} NMR (126 MHz, CDCl₃) δ 151.3, 141.6 (d, J_CP = 2.8 Hz), 138.2, 135.4 (d, J_CP = 11.6 Hz), 133.1 (d, J_CP = 17.3 Hz), 129.6 (d, J_CP = 10.6 Hz), 128.6, 125.4, 125.0, 33.5 (d, ¹J_CP = 34.7 Hz), 29.6 (d, ²J_CP = 2.9 Hz), 28.4, 26.5 (d, ³J_CP = 6.7 Hz), 26.4 (d, ³J_CP = 3.9 Hz), 25.9, 17.5, 14.8, 14.4, 11.9, 10.5 (br) ppm; ³¹P{¹H} NMR (202 MHz, CDCl₃) δ 51.6 ppm; ¹¹B{¹H} NMR (128 MHz, CDCl₃) δ −2.1 ppm; IR (neat): [small nu, Greek, tilde] = 2924 (m), 2851 (w), 1552 (s), 1447 (m), 1359 (m), 1324 (s), 1263 (w), 1173 (s), 1147 (s), 945 (s) cm⁻¹; HRMS (EI⁺) calcd for C₃₇H₅₃B₁N₂P₁Au₁Cl₁ [M − H]⁺ requires m/z 798.3424, found m/z 798.3426 (0.2 ppm).

X-ray crystallography

Data were collected at 150 K (120 K for 2a) on an Agilent Technologies Gemini A Ultra diffractometer with MoKα (λ = 0.71073 Å, for 4a, 5a structures A and B, and 9b) or CuKα (λ = 1.54178 Å, for 4b, 6a, and 8a) radiation,⁴¹ and on a Crystal Logics diffractometer equipped with a Rigaku Saturn 724+ detector at beamline I19 of Diamond Light Source using a synchrotron X-ray wavelength of 0.6889 Å (for 2a, 7b, and 9a).⁴² Selected crystallographic information is given in Table 2. Absorption corrections were based on multiple and symmetry-equivalent data; the structures were solved by direct and heavy-atom methods, and refined on all unique F² values with appropriate constraints and/or restraints in each case, particularly for the treatment of disordered structural components.⁴³ Unidentified solvent and/or counter-ion in the structure of the complex obtained from the attempted recrystallization of 4a was treated by the Squeeze procedure of PLATON;⁴⁴ H atoms could not be observed in difference maps for this relatively low-precision structure, so it is not clear whether the complex is a neutral Cu(II) complex with two ethoxide ligands or a cationic Cu(I) complex with two ethanol ligands and a highly disordered small anion, though the latter is more likely from the observed tetrahedral geometry. Further discussion and evidence from spectroscopic data is provided in the ESI.† CCDC references: 987389 (2a), 987388 (4a), 987387 (4b), 987386 (5aA), 987385 (5aB), 987390 (6a), 987384 (7b), 987391 (8a), 987383 (9a) and 987382 (9b).

Table 2 Crystallographic data

Compound	2a	4a	4b	5a (structure A)	5a (structure B)
Chemical formula	C47H46BN2P	C98H102B2CuN4O2P2	C76H90B2CuN4OP2^+·PF6^−	C96H119B2CuN5P2^+·PF6^−·C4H10O·2CHCl3	C94H116B2CuN4P2^+·PF6^−·2CHCl3
Formula mass	680.6	1514.9	1367.6	1947.9	1832.7
Crystal system	Monoclinic	Monoclinic	Triclinic	Triclinic	Monoclinic
a/Å	29.596(7)	22.626(2)	10.7978(6)	11.2490(2)	13.7756(6)
b/Å	8.231(2)	10.2574(8)	12.4349(7)	17.1875(4)	10.2495(5)
c/Å	31.073(12)	20.8126(19)	28.2720(15)	26.6167(6)	33.6122(17)
α/°			80.643(4)	93.8881(19)
β/°	102.186(2)	111.403(10)	86.405(4)	93.6056(17)	91.672(4)
γ/°			72.103(5)	92.9238(19)
Unit cell volume/Å^3	7399(4)	4497.2(7)	3564.0(4)	5116.22(19)	4743.8(4)
Space group	I2/a	P2/c	P1̄	P1̄	P2/c
Z	8	2	2	2	2
μ/mm^−1	0.075	0.327	1.575	0.476	0.508
No. of reflections measured	28 804	32 492	21 401	83 501	30 847
No. of independent reflections	6727	7915	11 052	20 525	9235
R int	0.0601	0.1080	0.0392	0.0496	0.0394
R (F, F^2 > 2σ)	0.0457	0.0803	0.0617	0.0728	0.0827
R w (F^2, all data)	0.1133	0.2213	0.1729	0.2236	0.2228
Goodness of fit on F^2	1.065	1.033	1.035	1.023	1.072
Difference map extremes/e Å^−3	0.32, −0.27	0.39, −0.41	0.72, −0.38	1.69, −1.32	1.28, −0.64

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Compound	6a	7b	8a	9a	9b
Chemical formula	C99H93AgB2F6N4O2P2	C79H109AgB2F6N4O2P2	C47H46AuBClN2P2·CHCl3	C47H58AuBClN2P·0.5C4H10O	C37H54AuBClN2P·CHCl3
Formula mass	1676.2	1452.1	1032.4	962.2	920.4
Crystal system	Monoclinic	Monoclinic	Orthorhombic	Triclinic	Monoclinic
a/Å	17.8281(6)	34.386(6)	9.5273(7)	8.9183(14)	18.2559(8)
b/Å	16.4975(4)	10.3299(19)	15.9516(10)	15.431(3)	9.4353(4)
c/Å	28.2893(12)	24.444(5)	28.6394(14)	17.126(3)	23.1349(10)
α/°				106.221(2)
β/°	93.976(5)	107.786(2)		91.812(2)	93.337(4)
γ/°				97.007(2)
Unit cell volume/Å^3	8300.4(5)	8268(3)	4352.5(5)	2240.8(7)	3978.2(3)
Space group	I2/a	C2/c	P212121	P1̄	P21/c
Z	4	4	4	2	4
μ/mm^−1	2.857	0.285	9.234	3.110	4.036
No. of reflections measured	13 509	35 858	11 804	23 163	40 350
No. of independent reflections	6411	9121	6623	10 658	9004
R int	0.0417	0.1189	0.0477	0.0431	0.0409
R (F, F^2 > 2σ)	0.0476	0.0839	0.0544	0.0432	0.0307
R w (F^2, all data)	0.1272	0.2293	0.1495	0.0964	0.0668
Goodness of fit on F^2	0.958	1.019	1.002	1.098	1.059
Difference map extremes/e Å^−3	0.59, −0.54	0.82, −0.85	3.13, −1.66	1.49, −1.09	1.35, −1.10

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Acknowledgements

We thank Newcastle University for funding (L. H. D.) and the EPSRC for a Career Acceleration Fellowship (L. J. H.), an equipment grant (W. C.), their National Mass Spectrometry Service Centre, Swansea, UK, and the Newcastle-operated synchrotron component of their National Crystallography Service. We also thank Diamond Light Source for access to synchrotron facilities. We are grateful to Johnson Matthey for the loan of certain precious metal salts.

Notes and references

1. (a) F. L. Thorp-Greenwood, Organometallics, 2012, 31, 5686–5692; (b) H. Kobayashi, M. Ogawa, R. Alford, P. L. Choyke and Y. Urano, Chem. Rev., 2009, 110, 2620.
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Footnote

† Electronic supplementary information (ESI) available: Experimental methods, spectroscopic and crystallographic characterisation, photophysical measurements and molecular modelling details. CCDC 987389, 987388, 987387, 987386, 987385, 987390, 987384, 987391, 987383 and 987382. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4dt00704b

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