Calcium complexes with imino-phosphinanilido chalcogenide ligands for heterofunctionalisation catalysis

Abstract

The syntheses, characterisation and utilisation of the calcium complexes [{L^x}CaN(SiMe₃)₂·(THF)] supported by monoanionic, tridentate imino-phosphinanilido chalcogenide ligands {Ph₂P(E)–N–C₆H₄–CH=N(Dipp)}⁻ (E = S, {L²}⁻; E = Se, {L³}⁻; Dipp = 2,6-diisopropylphenyl) as molecular precatalysts for the heterofunctionalisation of styrene are reported. The protio-ligand {L¹}H (for E = O) was obtained upon reaction of the aniline-iminophosphane {Ph₂PHN–C₆H₄–CH=N(Dipp)} ({L⁰}H) and hydrogen peroxide at room temperature. The related sulphide and selenide compounds {L²}H and {L³}H were prepared by treatment of {L⁰}H with elemental sulphur and selenium. Beside, reaction of {L⁰}H with Me₂S·BH₃ yielded the corresponding imino-phosphinanilido borane protio-ligand {Ph₂P(BH₃)N–C₆H₄–CH=N(Dipp)}H ({L⁴}H). The heteroleptic calcium complexes [{L^x}CaN(SiMe₃)₂·(THF)] (E = S, 2; E = Se, 3) were synthesised by one-pot reaction of {L²}H and {L³}H with 2 equiv of [KN(SiMe₃)₂] and CaI₂ at room temperature. The reaction of {L²}H with [KN(SiMe₃)₂] and CaI₂ in 2 : 2 : 1 proportions yielded the homoleptic complex [Ca{L²}₂] (5). The molecular structures of the protio-ligand {L³}H and complexes 3 and 5 were established by single crystal X-ray analysis. The heteroleptic complexes 2 and 3 constitute moderately efficient precatalysts for the intermolecular hydrophosphination and hydroamination of styrene with diphenylphosphine or pyrrolidine, respectively, to mediate the formation of C–P and C–N σ-bonds.

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Introduction

Catalysed heterofunctionalisations of unsaturated substrates (alkenes, carbonyls) continue to receive significant attention, primarily because of their 100% atom efficiency.¹ Alkene hydroamination (C–N σ-bond formation) and hydrophosphination (C–P σ-bond formation) have attracted a great deal of attention in recent years, not least because the resulting amines and phosphines constitute valuable products for a plethora of applications. Substantial advances were achieved for intramolecular hydroamination in the 1990s with alkali or transition metal complexes.^2,3 Most prominently for oxophilic metals, Mark's lanthanide(III) catalysts are remarkable for their efficiency in the cyclisation of aminoalkenes, aminoalkynes⁴ and in the cyclohydrophosphination of phosphinoalkenes.⁵ More recently, the cyclohydroamination of aminoalkenes was catalysed by d⁰ complexes of the alkalino-earth metals (Ae) as shown by Hill,⁶ Roesky,⁷ Sarazin/Carpentier⁸ and Ward.⁹ These groups have developed various original heteroleptic Ae complexes of the type [{L}Ae(X)(solvent)_n], where Ae is Ca, Sr or Ba, {L}⁻ is a monoanionic ancillary ligand such as a β-diketiminate, bis-phosphinomethanide, bis(imino)pyrrolide, aminotroponiminate, tris(pyrazolyl)borate, iminoanilide or aminoetherphenolate, and X⁻ is a reactive group such as an amide (e.g. N(SiMe₃)⁻ or N(SiMe₂H)⁻) or, sometimes, an alkyl (CH(SiMe₃)₂⁻). The bulky ancillary ligand is essential to control the kinetic lability of these complexes and tame their propensity to engage in deleterious ligand redistribution (Schlenk-like) equilibria.^6–10

The catalytic activity of these precatalysts built around large, electropositive Ae ions compares well with that of isoelectronic trivalent lanthanide systems. The calcium complex [{BDI}CaN(SiMe₃)₂·(THF)] ({BDI} = HC{C(Me)N-2,6-(ⁱPr)₂C₆H₃}₂) proved a very versatile and effective precatalyst not only for intramolecular hydroaminations, but also for the more challenging intermolecular hydrophosphination of alkynes and activated alkenes.^6,11 Several other heteroleptic calcium, strontium and barium complexes supported by a related iminoanilido or aminoetherphenolato ligands have also been reported for the intermolecular hydroamination and hydrophosphination of activated alkenes.⁸

In the course of our ongoing research into the chemistry of heavy alkaline earths, we have recently introduced a series of amidophosphine-chalcogenides/boranes [R₂NHPh₂P(E)]_n (R = bulky alkyl; E = O, S, Se, BH₃; n = 1 or 2) and sterically demanding nitrogen ancillary ligands [2-(Ph₃CN=CH)C₄H₃NH] into alkali and alkalino-earth metal coordination chemistry.¹² In all cases, the ligand with multiple donor atoms stabilised the oxophilic ions, and the molecular structures of the resulting complexes were authenticated. The Ae compounds showed excellent catalytic activity towards the ring-opening polymerisation of ε-caprolactone. However, the major disadvantage of these ligands was their relatively limited ability to prevent ligand redistribution in solution. Thus, we were led to conclude that greater steric bulkiness might be necessary to prevent these deleterious equilibria from taking place. To circumvent this problem, sterically more demanding multidentate monoanionic ligands were devised for the kinetic stabilisation of heteroleptic Ae complexes. We report here the syntheses of imino-phosphinanilido chalcogenides {Ph₂P(E)–N–C₆H₄–CH=N(Dipp)}H (E = O, {L¹}H; S, {L²}H; Se, {L³}H; Dipp = 2,6-diisopropylphenyl) and imino-phosphinanilidoborane {Ph₂P(BH₃)N–C₆H₄–CH=N(Dipp)}H ({L⁴}H) along with the syntheses and structural aspects of the calcium complexes [{L^x}CaN(SiMe₃)₂·(THF)] (E = S, x = 2, 2; E = Se, x = 3, 3) and [Ca{L²}₂] (5). The ability of 2 and 3 to catalyse the intermolecular hydrophosphination and hydroamination of styrene is also presented.

Results and discussion

Synthesis and characterisation

The phosphinanilido-imine precursor {Ph₂PHN–C₆H₄–CH=N(Dipp)} ({L⁰}H) was readily obtained in good yield and high purity by equimolar aminolysis of chlorodiphenylphosphine with {H₂NC₆H₄CH=N(Dipp)} in toluene at room temperature, using a slight excess of triethylamine to trap the released HCl (Scheme 1).

Scheme 1 Synthesis of imino-phosphinanilido chalcogenides and borane protio-ligands {L^x}H, x = 1–4.

The precursor {L⁰}H was characterised by conventional techniques. In the ¹H NMR spectrum, the signal for the amine NH hydrogen atom appears at δ_¹H = 10.28 ppm as a doublet due to coupling with the phosphorus atom (²J_HP of 9.1 Hz). The resonance for the imine proton appears as a singlet at δ_¹H = 8.27 ppm. In the ³¹P NMR spectrum, the compound exhibits a sharp singlet at δ_³¹P = 23.3 ppm.

The oxide ligand {L¹}H was prepared in 85% yield by treatment of {L⁰}H with hydrogen peroxide, whereas the action of elemental sulphur and selenium onto {L⁰}H afforded the corresponding sulphide {L²}H and selenide {L³}H congeners in yields above 85% (Scheme 1). The borane adduct {L⁴}H was isolated in quantitative yield as yellow precipitate by the reaction of {L⁰}H and Me₂S·BH₃ in toluene (Scheme 1). These protio-ligands were characterised by multinuclear NMR and combustion analysis. In the ¹H NMR spectra, the amine NH hydrogen atom can be seen at δ_¹H = 11.41–11.44 ppm as a doublet with ²J_HP coupling constants of 13.7 for {L¹}H, 10.2 for {L²}H, and 9.0 Hz for {L³}H. In {L⁴}H, its resonance is seen at δ_¹H = 11.19 ppm, with ²J_HP = 4.0 Hz. In all cases, there is hence a significant downfield shift as compared with {L⁰}H. In their ³¹P{¹H} NMR spectra, {L²}H and {L³}H exhibit similar resonances at δ_³¹P = 49.8 and 45.0 ppm, respectively. This is shifted downfield compared to the data for {L¹}H (δ_³¹P = 19.0 ppm), presumably due to the adjacent hard oxygen atom. However, the borane derivative {L⁴}H displays an even more downfield broad resonance signal at δ_³¹P = 65.8 ppm. Additionally, in the ¹¹B{¹H} NMR spectrum, a broad resonance signal at δ_¹¹B = −36.0 ppm was detected for the P–BH₃ moiety. These observations indicate that the BH₃ group formed the phosphine-borane adduct rather than the amine-borane one. The selenium-containing {L³}H was characterised by ⁷⁷Se{¹H} NMR spectroscopy; it features a doublet at δ_⁷⁷Se = −251 ppm, with a ¹J_SeP coupling constant of 776 Hz which matches that measured in this compound's ³¹P{¹H} NMR spectrum (Fig. 1).

Fig. 1 ⁷⁷Se{¹H} NMR (CDCl₃, 76.31 MHz, 25 °C) (top right) and ³¹P{¹H} NMR (CDCl₃, 161.9 MHz, 25 °C) spectra for {Ph₂P(Se)–N–C₆H₄–CH=N(Dipp)}H ({L³}H).

The solid state structure of {L³}H was established by single crystal X-ray diffraction. Its molecular structure is depicted in Fig. 2. The P–Se bond distance of 2.0930(7) Å is very similar to that previously reported for [Ph₂P(Se)-NH(2,6-Me₂C₆H₃)]¹³ (2.1019(8) Å) and is hence diagnostic of P=Se double bonds. The P–N bond distance of 1.662(2) Å is consistent with those measured in other phosphinamines.^12,13

Fig. 2 Molecular solid-state structure of {Ph₂P(Se)–N–C₆H₄–CH=N(Dipp)}H ({L³}H). Hydrogen atoms except that on N1 are omitted for clarity. Selected bond lengths (Å) and angles (°): Se1–P1 2.0933(7), P1–N1 1.662(2), N2–C7 1.264(3), N1–C1 1.384(3), N1–P1–Se1 117.11(9), C1–N1–P1 129.59(2), N1–C1–C6 119.1(2), C7–N2–C8 119.8(2).

Using a known strategy,⁸ the one-pot reaction of {L²}H with [KN(SiMe₃)₂] in THF followed by the addition of CaI₂ (in 1 : 2 : 1 molar ratio) cleanly yielded the desired heteroleptic complex [{L²}CaN(SiMe₃)₂·(THF)] (2) in 75% yield. The analogous reaction with the selenide {L³}H afforded analytically pure [{L³}CaN(SiMe₃)₂·(THF)] (3) in 71% yield (Scheme 2). However, all attempts to prepare the congeneric complex [{L¹}CaN(SiMe₃)₂·(THF)] (1) using the oxygen-containing {L¹}H proved unsuccessful and gave intractable mixtures of unidentified species, presumably because of issues stemming from the combined presence of the phosphine oxide with oxophilic element such as calcium. Note also that, similarly, the use of the borane ligand {L⁴}H afforded a complex with the putative formulation [{L⁴}CaN(SiMe₃)₂·(THF)] (4), but NMR data were inconclusive and the composition could not be confirmed by elemental analysis either. Nonetheless, analysis of a small crop of single crystals by XRD techniques confirmed the proposed formulation, and showed coordination of two of the three hydrogen atoms in the borane moiety onto the calcium center; a representation of the molecular structure and the XRD data for 4 is available in the ESI.†

Scheme 2 Synthesis of the heteroleptic calcium complexes [{L²}CaN(SiMe₃)₂·(THF)] (2) and [{L³}CaN(SiMe₃)₂·(THF)] (3).

Complexes 2 and 3 were characterised by multinuclear NMR spectroscopy and elemental analysis, and the solid-state structure of 3 was confirmed by X-ray diffraction analysis. In the ¹H NMR spectra recorded in C₆D₆, the resonance for the imine proton appears at δ_¹H = 7.91 and 7.92 ppm for complexes 2 and 3 respectively, i.e. slightly shifted towards high fields with respect to the protio-ligands (δ_¹H = 8.26 and 8.27 ppm); the presence of one molecule of coordinated THF per metal is unambiguous. In the ³¹P{¹H} NMR spectra, sharp resonances were detected at δ_³¹P = 40.6 (for 2) and 31.1 ppm (for 3, Fig. 3), i.e. at higher field than in the respective protio-ligands. In the ⁷⁷Se{¹H} NMR spectra of 3 (Fig. 3), a doublet was observed at δ_⁷⁷Se = −61 ppm, with a coupling constant ¹J_SeP of 589 Hz. The substantial low-field shift and the lower coupling constant compared to the pertaining data for {L³}H are indicative of coordination of the selenium atom onto the calcium ion in 3.

Fig. 3 ⁷⁷Se{¹H} NMR (C₆D₆, 76.31 MHz, 25 °C) (top right) and ³¹P{¹H} NMR (C₆D₆, 161.9 MHz, 25 °C) spectra for [{L³}CaN(SiMe₃)₂·(THF)] (3).

X-ray quality crystals of complex 3 were grown at −30 °C from a concentrated pentane solution, and its structure was determined (Fig. 4). The κ³-coordination mode of the ligand is plain in the structure of 3, and the corresponding metric parameters are diagnostic. The additional presence of coordinated THF takes the formal coordination number around Ca to five.

Fig. 4 Solid-state structure of [{L³}CaN(SiMe₃)₂·(THF)] (3). All hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): Ca1–N1 2.395(5), Ca1–N41 2.369(4), Ca1–N21 2.502(5), Ca1–Se1 3.016(2), Ca1–O11 2.387(4), Ca1–P1 3.240(2), Se1–P1 2.152(1), N41–P1 1.616(4), N21–C34 1.276(7), N1–Ca1–O11 100.26(2), N1–Ca1–N41 112.92(2), O11–Ca1–N41 146.61(1), N1–Ca1–N21 129.02(2), O11–Ca1–N21 89.09(1), N41–Ca1–N21 73.23(1), N41–Ca1–Se1 120.66(1), O11–Ca1–Se1 93.43(1), N41–Ca1–Se1 67.01(1), N21–Ca1–Se1 108.44(1), N1–Ca1–P1 113.94(1), O11–Ca1–P1 131.62(1), N41–Ca1–P1 28.64(1), N21–Ca1–P1 94.33(1), Se1–Ca1–P1 40.04(3).

The arrangement around the calcium ion is intermediate between a square base pyramidal and trigonal bipyramidal. However, with a geometric parameter of τ₅ = 0.63,¹⁴ the geometry around the metal ion can be best described as a highly distorted trigonal bipyramidal with N1, N21 and Se1 sitting in equatorial positions and O1 and N41 in axial ones. The dihedral angle of 53.2° between the two planes defined by N21, Ca1, N41, C34 and Ca1, Se1, P1, N1 indicates that the two metallacycles are not coplanar. The distance from Ca1 to the imine N2 atom (2.502(5) Å) is greater than that to the amido N1 (2.329(5) Å) and N3 (2.396(4) Å) atoms; the discrepancy between the Ca1–N1 and Ca1–N3 bond lengths reflects the formation of the Ca1–N1–P1–Se1 metallacycle, and the bulkiness of the hexamethyldisilazide group. The Ca1–Se1 distance of 3.0164(16) Å compares with those in [Ca{Ph₂P(Se)N(CHPh₂)}₂·(THF)₂] (2.989(8) Å)^12a and [Ca{(PyCH)(Se)PPh₂}₂(THF)₂] (2.945(1) Å),¹⁵ but it is much shorter than in [Ca{Ph₂P(Se)–NCH₂CH₂NPPh₂(Se)}·(THF)₃] (3.252(2) Å) where the calcium centre is 7-coordinate.^12d

The homoleptic complex [Ca{L²}₂] (5) was prepared in 67% yield by the one-pot treatment of {L²}H, [KN(SiMe₃)₂] and CaI₂ in 2 : 2 : 1 molar ratio in THF (Scheme 3). The analytical data (NMR, combustion analysis) testify to its purity and show that no THF is found in the complex.

Scheme 3 Synthesis of the homoleptic complex [Ca{L²}₂] (5).

Its molecular structure was determined by single crystal X-ray diffraction, and showed a six-coordinate calcium centre sitting in a distorted octahedral environment (N2–Ca1–N2ⁱ 173.00°) where both ligands feature κ³-coordination (Fig. 5). The details of structural parameters are available in Table TS1 in the ESI.† In complex 5, a coordination number of six is reached by κ³-coordination of the two monoanionic {Ph₂P(S)NH–C₆H₄CH=N(Dipp)}⁻ moieties. The Ca1–S distances of 2.8372(5) Å are expectedly shorter than the Ca–Se distance (3.0164(16) Å) observed in 3, but it resembles that in [Ca(S-2,4,6-tBu₃-C₆H₂)₂(THF)₄] (2.8177(8) Å).¹⁶ The solid-state structure of complex 5 is consistent with its NMR spectra in solution, as only one set of resonances was detected in the spectra recorded in C₆D₆. A singlet resonance at δ_¹H = 7.88 ppm was observed for the two imine (N=CH) protons. The 2,6-diisopropyl groups in the ligand gave rise to a septet at δ_¹H = 2.89 ppm for CH(CH₃)₂ hydrogen atoms and a broad doublet centred on 1.07 ppm for the methyl moieties. In the ³¹P NMR spectrum, a singlet at δ_³¹P = 62.6 ppm was observed, i.e. at much lower field than in 2 or in the protio-ligand.

Fig. 5 Representation of the molecular solid-state structure of [Ca{L²}₂] (5). All hydrogen atoms are omitted for clarity. Selected bond lengths (Å): Ca1–N1 2.451(1), Ca1–N1ⁱ 2.451(1), Ca1–N2ⁱ 2.465(1), Ca1–N2 2.465(1), Ca1–S1 2.837(5), Ca1–S1ⁱ 2.837(5), Ca1–P1ⁱ 3.189(4), Ca1–P1 3.189(4), S1–P1 1.981(6), P1–N2 1.629(1).

Hydroelementation reactions

Preliminary investigations on the performance of the heteroleptic complexes 2 and 3 as precatalysts for the benchmark intermolecular hydrophosphination and hydroamination of styrene were carried out. In a first set of experiments, the addition of Ph₂PH to styrene was examined with a precatalyst loading of 2.0 mol%, with [styrene]₀/[HPPh₂]₀/[Ca]₀ = 50 : 50 : 1. Characteristically for calcium,¹⁷ it was found that the reaction was fully regioselective, and afforded exclusively the anti-Markovnikov product (Scheme 4).

Scheme 4 Intermolecular hydrophosphination of styrene with diphenylphosphine catalysed by 2 and 3.

The reaction proceeds smoothly using complex 3 as precatalyst in neat condition, achieving near-complete conversion of 50 equiv. of neat substrates in 12 h (Table 1, entries 1–5). It also converted 53% of 400 equiv. of substrates in the same amount of time (entry 9), with a corresponding TOF of 18 mol_subst mol_Ca⁻¹ h⁻¹. Precatalyst 2 was equally competent, compare entries 5 and 6.

Table 1 Catalytic hydrophosphination of styrene with phosphine catalysed by 2 and 3 ^a

Entry	Precat.	Time (h)	Conversion (%)	Solvent
a All reactions performed at 60 °C, using 2.0 mol% of precatalyst unless otherwise stated.b Reactions in 0.3 mL of C6D6 at 0.51 mM in substrates.c Precatalyst loading = 0.25 mol%.
1	3	1	16	—(neat)
2	3	2	23	—(neat)
3	3	4	32	—(neat)
4	3	6	47	—(neat)
5	3	12	93	—(neat)
6	2	12	94	—(neat)
7^b	2	2	8	C6D6
8^b	2	24	22	C6D6
9 ^c	3	12	53	—(neat)

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By contrast, the reactions were slower when performed in C₆D₆ (entries 7–8). The poor conversion after 24 h perhaps reflects catalyst decomposition under prolonger reaction time under these experimental conditions. Only two calcium complexes, [{DippNCHN(Dipp)}CaN(SiMe₃)₂(THF)] and [{BDI}CaN-(SiMe₃)₂(THF)], displayed overall better catalytic activity in this reaction than complexes 2 and 3.^6,8

Complex 3 was next employed to catalyse the equimolar hydroamination of styrene with pyrrolidine, using again a standard metal feed ratio of [styrene]₀/[pyrrolidine]₀/[Ca]₀ = 50 : 50 : 1. The reactions were carried out in the temperature range 60–100 °C, either in neat substrates or in aromatic solvents (Table 2). The catalysed reactions were regiospecific, affording solely the anti-Markovnikov addition product. At 60 °C, the conversion reached 38% after 2 h at 60 °C (entry 1), and only modest progress was observed beyond this time (entries 2–4); even after 24 h, only half of the substrates were converted (entry 5), suggesting catalyst deactivation. Only at 110 °C could significantly higher conversions be observed (entries 6–7); in that case also, the conversion reached a maximum of ca. 77–79%, no matter the reaction was performed for 6 or 12 h. This suggests that, at higher temperature, the hydroelementation reaction is favoured over the putative decomposition process, but decomposition could eventually not be totally prevented. The reactions were also sluggish in dilute C₆D₆ or toluene-d₈ solutions (entries 8 and 10) (Scheme 5). Hence the catalytic activity displayed by 3 in intermolecular hydroamination is rather tame, and compares unfavourably with that of other calcium precatalysts.^6–10 Complex 2 showed very much the same performance as 3.

Table 2 Hydroamination of styrene with pyrrolidine catalysed by calcium complex 3 ^a

Entry	Temp. (°C)	Time (h)	Conversion (%)	Solvent
a All reactions performed using 2.0 mol% of precatalyst 3 unless otherwise stated.b Reactions in 0.3 mL of C6D6 at 0.51 mM in substrates.
1	60	2	38	—(neat)
2	60	3	39	—(neat)
3	60	4	43	—(neat)
4	60	12	49	—(neat)
5	60	24	50	—(neat)
6	110	6	77	—(neat)
7	110	12	79	—(neat)
8^b	80	12	40	C6D6
9	80	12	66	—(neat)
10	110	6	42	Tol-d8

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Scheme 5 Intermolecular hydroamination of styrene with pyrrolidine catalysed by the calcium complex 3.

Conclusion

Tridentate monoanionic imino-phosphinanilido chalcogenide ligands have been introduced for the first time in calcium chemistry, and have enabled the preparation of heteroleptic calcium–amide complexes. The molecular solid-state structures of the two calcium complexes 3 and 5 confirm that the ligand adopts a κ³-coordination mode, with effective coordination of the chalcogen onto the calcium ion. The heteroleptic complexes 2 and 3 showed good performance in the anti-Markovnikov intermolecular hydrophosphination of styrene, but low activity in the intermolecular hydroamination of that same substrate. It was in particular found that the nature of the chalcogen element in the ancillary ligand had little role in the ability of the resulting complex to mediate with two benchmark reactions, highlighting the limited ability of these soft atoms to influence the coordination sphere of the hard, oxophilic calcium ion.

Experimental

General

All manipulations were performed under an inert atmosphere using standard Schlenk techniques or in a dry, solvent-free glove box (Jacomex; O₂ < 1 ppm, H₂O < 5 ppm) for catalyst loading. CaI₂ (Aldrich, 99.999% anhydrous beads) and HPPh₂ were used as received. Styrene was dried and distilled over CaH₂ and stored over 3 Å molecular sieves. Compounds [O₂NC₆H₄CH=N(Dipp)],¹⁸ and [H₂NC₆H₄CH=N(Dipp)]¹⁹ were prepared by following literature protocols. Solvents (THF, Et₂O, pentane, and toluene) were purified and dried (water contents all below 10 ppm) over alumina columns (MBraun SPS). THF was further distilled under argon from sodium mirror/benzophenone ketyl prior to use. All deuterated solvents (Eurisotop, Saclay, France) were stored in sealed ampules over activated 3 Å molecular sieves and were thoroughly degassed by several freeze–thaw–vacuum cycles. NMR spectra were recorded on Bruker AM-400 and AM-500 spectrometers. All ¹H, ³¹P{¹H}, and ¹³C{¹H} chemical shifts were determined using residual signals of the deuterated solvents and were calibrated vs. SiMe₄ and ⁷⁷Se{¹H} NMR spectra were externally calibrated vs. Ph₂Se₂ (δ_⁷⁷Se = +461 ppm). Assignment of the signals was carried out using 1D (¹H, ¹³C{¹H}) and 2D (COSY, HMBC, HMQC) NMR experiments. Coupling constants are given in hertz. Elemental analyses were performed on a Bruker Euro EA and high-resolution mass spectra (HR-MS) were recorded on an Agilent 6538 UHD Q-TOF using multimode source at the Indian Institute of Technology Hyderabad (IITH), or on a Bruker MaXis 4 G using electrospray or ASAP sources at the University of Rennes 1.

Ph₂PHNC₆H₄CH=N(Dipp)] ({L⁰}H). Triethylamine (1.5 mL, 12.8 mmol) and chlorodiphenylphosphine (1.9 mL, 10.7 mmol) were added to a solution of [H₂NC₆H₄CH=N(Dipp)] (3.0 g, 10.7 mmol) in toluene (50 mL). Immediate formation of a white turbidity was observed. The reaction mixture was stirred overnight at room temperature. The insoluble fraction (white solid, ammonium salt) was eliminated by cannula filtration. Toluene was then removed in vacuo, giving a brown sticky solid which was washed with pentane (2 × 20 mL) to yield the title compound as an analytically pure pale yellow solid. Yield 4.1 g, 83%.

¹H NMR (CDCl₃, 500.13 MHz, 25 °C): δ = 10.28 (d, ³J_HP = 9.1 Hz, 1H; NH), 8.27 (s, 1H; CH=N), 7.75 (dd, ³J_HH = 8.3 Hz, ⁴J_HH = 5.0 Hz, 1H; NC₆H₃), 7.49 (complex m, 4H; PC₆H₅), 7.36 (m, 2H; PC₆H₅), 7.29 (overlapping m, 6H; PC₆H₅ and C₆H₄), 7.13 (complex m, 3H; NC₆H₃ and C₆H₄), 6.84 (t, ³J_HH = 7.4 Hz, 1H; C₆H₄), 2.94 (sept, ³J_HH = 8 Hz, 2H; CH(CH₃)₂), 1.08 (d, ³J_HH = 6.9 Hz, 12H; CH(CH₃)₂) ppm; ¹³C{¹H} NMR (C₆D₆, 125.76 MHz, 25 °C): δ = 166.2 (CH=N), 150.0 (i-NC₆H₃), 148.4 (i-NC₆H₄), 139.9 (i-PC₆H₅), 138.1 (o-NC₆H₃), 134.6 (C₆H₄), 132.1 (p-NC₆H₃), 132.1 (p-NC₆H₃), 131.2 (o-PC₆H₅), 131.1 (o-PC₆H₅), 128.8 (m-PC₆H₅), 128.3 (m-PC₆H₅), 124.8 (m-NC₆H₃), 119.0 (C₆H₄), 117.3 (C₆H₄), 115.1 (C₆H₄), 114.9 (C₆H₄), 27.9 (CH(CH₃)₂), 23.4 (CH(CH₃)₂) ppm; ³¹P{¹H} NMR (CDCl₃, 161.9 MHz, 25 °C): δ = 23.3 ppm. Elem. anal. calcd for C₃₁H₃₃N₂P (464.6 g mol⁻¹): C, 80.14; H, 7.16; N, 6.03. Found: C, 79.88; H, 7.01; N, 5.81. ESI-HRMS: [M + H⁺] (C₃₁H₃₄N₂P) calcd m/z 465.2459, found 465.2458.

[Ph₂P(O)HNC₆H₄CH=N(Dipp)] ({L¹}H). A 30% solution of H₂O₂ (0.15 mL, 5 mmol) in water was added to a toluene solution (30 mL) of {L⁰}H (2.0 g, 4.3 mmol). The reaction mixture was stirred for 6 h at room temperature. After removal of solvent, a half white solid residue was obtained which was washed with pentane (2 × 10 mL) to yield the title compound as an off-white solid. Yield 1.70 g, 85%.

¹H NMR (CDCl₃, 500.13 MHz, 25 °C): δ = 11.41 (d, ²J_HP = 13.7 Hz, 1H; NH), 8.30 (s, 1H; CH=N), 7.88 (dd, ³J_HH = 12.5 Hz, ⁴J_HH = 7.5 Hz, 4H; PC₆H₅), 7.49 (t, ³J_HH = 7.6 Hz, 3H; NC₆H₃ and PC₆H₅), 7.41 (m, 5H; PC₆H₅ and C₆H₄), 7.27 (d, ³J_HH = 10.1 Hz, 1H; C₆H₄), 7.14 (s, 3H; NC₆H₃ and C₆H₄), 6.99 (t, ³J_HH = 7.5 Hz, 1H; C₆H₄), 2.93 (sept, ³J_HH = 8 Hz, 2H; CH(CH₃)₂), 1.09 (d, ³J_HH = 6.8 Hz, 12H; CH(CH₃)₂) ppm. ¹³C{¹H} NMR (C₆D₆, 125.76 MHz, 25 °C): δ = 166.3 (CH=N), 147.7 (i-NC₆H₄), 143.6 (i-NC₆H₃), 138.1 (i-PC₆H₅), 134.4 (o-NC₆H₃), 132.8 (C₆H₄), 132.3 (o-PC₆H₅), 132.1 (o-PC₆H₅), 131.8 (p-PC₆H₅), 131.6 (p-PC₆H₅), 131.5 (p-NC₆H₃), 128.8 (m-PC₆H₅), 128.6 (m-PC₆H₅), 124.8 (m-NC₆H₃), 120.2 (C₆H₄), 119.9 (C₆H₄), 119.9 (C₆H₄), 118.5 (C₆H₄), 28.1 (CH(CH₃)₂), 23.3 (CH(CH₃)₂) ppm. ³¹P{¹H} NMR (CDCl₃, 161.9 MHz, 25 °C): δ = 19.0 ppm. Elem. anal. calcd for C₃₁H₃₃N₂PO (480.5 g mol⁻¹): C, 77.48; H, 6.92; N, 5.83. Found: C, 77.19; H, 6.73, N, 5.63. ESI-HRMS: [M + Na⁺] (C₃₁H₃₄N₂PO) calcd m/z 503.2228, found 503.2226.

[Ph₂P(S)HNC₆H₄CH=N(Dipp)] ({L²}H). {L⁰}H (2.0 g, 4.3 mmol) and elemental sulphur (138 mg, 4.3 mmol) were heated at 90 °C in toluene (30 mL) for 12 h. After evaporation of solvent, a pale yellow solid residue was obtained which was washed with pentane (2 × 10 mL) to yield the title compound as a pale yellow solid. Yield 1.9 g, 90%.

¹H NMR (CDCl₃, 500.13 MHz, 25 °C): δ = 11.41 (d, ²J_HP = 10.2 Hz, 1H; NH), 8.26 (s, 1H; CH=N), 7.97 (m, 4H; PC₆H₅), 7.47 (t, ³J_HH = 8.1 Hz, 2H; NC₆H₃ and C₆H₄), 7.43 (complex m, 2H; PC₆H₅), 7.38 (overlapping m, 5H; PC₆H₅ and C₆H₄), 7.10 (s, 3H; NC₆H₃ and C₆H₄), 6.98 (t, ³J_HH = 7.4 Hz, 1H; C₆H₄), 2.85 (sept, ³J_HH = 8 Hz, 2H; CH(CH₃)₂), 1.04 (d, ³J_HH = 6.8 Hz, 12H; CH(CH₃)₂) ppm. ¹³C{¹H} NMR (C₆D₆, 125.76 MHz, 25 °C): δ = 166.2 (CH=N), 147.5 (i-N=CHC₆H₄), 143.3 (i-NC₆H₃), 138.0 (i-PC₆H₅), 134.5 (o-PC₆H₅), 134.4 (o-PC₆H₅), 133.5 (o-NC₆H₃), 131.9 (p-PC₆H₅), 131.8 (p-PC₆H₅), 131.3 (C₆H₄), 131.2 (p-NC₆H₃), 128.7 (m-PC₆H₅), 128.6 (m-PC₆H₅), 124.8 (m-NC₆H₃), 120.5 (C₆H₄), 120.1 (NC₆H₄), 118.6 (C₆H₄), 28.1 (CH(CH₃)₂), 23.3 (CH(CH₃)₂) ppm. ³¹P{¹H} NMR (CDCl₃, 161.9 MHz, 25 °C): δ = 49.8 ppm. Elem. anal. calcd for C₃₁H₃₃N₂PS (496.6 g mol⁻¹): C, 74.97; H, 6.70; N, 5.64; S, 6.46. Found: C, 74.69; H, 6.43; N, 5.49; S, 6.35. ESI-HRMS: [M + Na⁺] (C₃₁H₃₄N₂PS) calcd m/z 519.1999, found 519.1998.

[Ph₂P(Se)HNC₆H₄CH=N(Dipp)] ({L³}H). {L⁰}H (2.0 g, 4.3 mmol) and elemental selenium (0.50 g, 6.45 mmol) were heated at 90 °C in toluene (30 mL) for 12 h. Un-reacted excess selenium was filtered off and the filtrate was collected. After evaporation of the solvent, a light yellow solid residue was obtained which was washed with pentane (2 × 10 mL) to yield the title compound as a pale yellow solid. Yield 2.0 g, 85%.

¹H NMR (CDCl₃, 500.13 MHz, 25 °C): δ = 11.44 (d, ²J_HP = 9 Hz, 1H; NH), 8.27 (s, 1H; CH=N), 7.98 (dd, ³J_HH = 14.1 Hz, ⁴J_HH = 7.1 Hz, 4H; PC₆H₅), 7.48 (overlapping m, 1H; NC₆H₃), 7.42 (overlapping m, 2H; PC₆H₅), 7.38 (complex m, 5H; PC₆H₅ and C₆H₄), 7.25 (m, mixed with solvent, 1H; C₆H₄), 7.10 (s, 3H; NC₆H₃ and C₆H₄), 7.0 (t, ³J_HH = 7.4 Hz, 1H; C₆H₄), 2.85 (sept, ³J_HH = 8 Hz, 2H; CH(CH₃)₂), 1.04 (d, ³J_HH = 6.7 Hz, 12H; CH(CH₃)₂) ppm. ¹³C{¹H} NMR (C₆D₆, 125.76 MHz, 25 °C): δ = 166.2 (CH=N), 147.4 (i-N=CHC₆H₄), 143.3 (i-NC₆H₃), 138.0 (i-PC₆H₅), 134.5 (o-NC₆H₃), 133.9 (o-NC₆H₃), 133.0 (o-PC₆H₅), 131.9 (p-PC₆H₅), 131.7 (p-PC₆H₅), 131.6 (C₆H₄), 131.5 (p-NC₆H₃), 128.7 (m-PC₆H₅), 128.5 (m-PC₆H₅), 124.8 (m-NC₆H₃), 120.7 (C₆H₄), 120.2 (NC₆H₄), 118.6 (C₆H₄), 28.0 (CH(CH₃)₂), 23.3 (CH(CH₃)₂) ppm. ³¹P{¹H} NMR (CDCl₃, 161.9 MHz, 25 °C): δ = 45.0 (¹J_PSe = 775 Hz) ppm. ⁷⁷Se{¹H} NMR (CDCl₃, 76.31 MHz, 25 °C): δ = −251 (d, ¹J_SeP = 776 Hz) ppm. Elem. anal. calcd for C₃₁H₃₃N₂PSe (543.5 g mol⁻¹): C, 68.50; H, 6.12; N, 5.15. Found: C, 68.55; H, 6.16; N, 5.03. ESI-HRMS: [M + Na⁺] (C₃₁H₃₄N₂PSe) calcd m/z 567.1444, found: 567.1442.

[Ph₂P(BH₃)NH–C₆H₄CH=N(Dipp) ({L⁴}H). To a toluene solution (20 mL) of ({L⁰}H) (2 g, 4.3 mmol), was added a borane-dimethyl sulphide (0.4 mL, 4.3 mmol) solution dropwise with stirring at room temperature. The reaction mixture was then stirred for another 12 h. The solvent toluene was evaporated in vacuo. The compound ({L⁴}H) was obtained after washing with pentane (2 × 10 mL) as yellow solid. Yield: 2.0 g, 97%.

¹H NMR (CDCl₃, 400 MHz, 298 K): δ = 11.19 (d, J_HP = 4.0 Hz, 1H; NH), 7.98 (s, 1H; CH=N), 7.95–7.90 (m, 4H; PC₆H₅), 7.68 (d, J_HH = 8, 1H; C₆H₄), 7.08 (t, ³J_HH = 7.6 Hz, 3H; NC₆H₃ and C₆H₄), 7.05–7.01 (complex m, 3H; PC₆H₅ and C₆H₄), 6.95–6.93 (m, 4H; PC₆H₅), 6.86 (dt, ³J_HH = 7.4 Hz, 1H; C₆H₄), 6.58 (dt, ³J_HH = 7.4 Hz, 1H; C₆H₄), 2.98 (sept, ³J_HH = 8 Hz, 2H; CH(CH₃)₂), 2.11 (br, 3H, BH₃), 1.06 (d, ³J_HH = 6.7 Hz, 12H; CH(CH₃)₂) ppm; ¹³C{¹H} NMR (C₆D₆, 125.8 MHz, 298 K): δ = 166.2 (CH=N), 147.4 (i-N=CHC₆H₄), 143.3 (i-NC₆H₃), 138.0 (i-PC₆H₅), 134.5 (o-NC₆H₃), 133.9 (o-NC₆H₃), 133.0 (o-PC₆H₅), 131.9 (p-PC₆H₅), 131.7 (p-PC₆H₅), 131.6 (C₆H₄), 131.5 (p-NC₆H₃), 128.7 (m-PC₆H₅), 128.5 (m-PC₆H₅), 124.8 (m-NC₆H₃), 120.7 (C₆H₄), 120.2 (NC₆H₄), 118.6 (C₆H₄), 28.0 (CH(CH₃)₂), 23.3 (CH(CH₃)₂) ppm; ³¹P{¹H} NMR (CDCl₃, 161.9 MHz, 298 K): δ = 65.8 ppm; ¹¹B{¹H} NMR (128.4 MHz, CDCl₃, 298 K): δ −36.05 ppm.

[{Ph₂P(S)NC₆H₄CH=N–(Dipp)}Ca{N(SiMe₃)₂}(THF)] (2). THF (20 mL) was added to a mixture of {L²}H (0.3 g, 0.60 mmol) and KN(SiMe₃)₂ (0.24 g, 1.2 mmol). The reaction mixture was stirred at room temperature for 1 h, and was then added to a suspension of CaI₂ (0.18 g, 0.60 mmol) in THF (20 mL). After stirring at room temperature for 12 h, the solvent was evaporated under vacuum and the residue was extracted with pentane (50 mL). After filtration to eliminate insoluble materials, volatiles were removed in vacuo to afford the title compound as a pale yellow solid. Yield (0.35 g, 75%).

¹H NMR (C₆D₆, 500.13 MHz, 25 °C): δ = 8.06 (m, 4H; PC₆H₅), 7.91 (s, 1H; CH=N), 7.11 (dd, ³J_HH = 7.6 Hz, ⁴J_HH = 2.8 Hz, 3H; NC₆H₃, PC₆H₅), 7.05 (m, 2H; NC₆H₃), 7.0 (s, 4H; PC₆H₅), 6.95(d, ³J_HH = 8.4 Hz, 1H, C₆H₄), 6.89 (d, ³J_HH = 7.7 Hz, 1H; C₆H₄), 6.74 (td, ³J_HH = 15.6 Hz, ⁴J_HH = 1.6 Hz, 1H; C₆H₄), 6.47 (t, ³J_HH = 7.4 Hz, 1H; C₆H₄), 3.41 (br s, 4H; OCH₂CH₂), 3.16 (sept, ³J_HH = 8 Hz, 2H; CH(CH₃)₂), 1.24 (d, ³J_HH = 6.8 Hz, 6H; CH(CH₃)₂), 1.08 (br s, 4H; OCH₂CH₂), 0.93 (d, ³J_HH = 6.7 Hz, 6H; CH(CH₃)₂), 0.38 (s, 18H, Si(CH₃)₃) ppm. ¹³C{¹H} NMR (C₆D₆, 125.76 MHz, 25 °C): δ = 171.5 (CH=N), 152.1 (i-N=CHC₆H₄), 152.0 (i-NC₆H₃), 149.6 (i-PC₆H₅), 139.5 (o-NC₆H₃), 136.1 (o-NC₆H₃), 132.8 (o-PC₆H₅), 131.5 (p-PC₆H₅), 130.5 (C₆H₄), 128.1 (p-PC₆H₅), 128.0 (p-NC₆H₃), 126.3 (m-NC₆H₃), 126.2 (m-PC₆H₅), 125.7 (m-PC₆H₅), 123.4 (m-PC₆H₅), 123.3 (C₆H₄), 123.2 (NC₆H₄), 118.2 (C₆H₄), 68.7 (OCH₂CH₂), 28.3 (CH(CH₃)₂), 25.3 (CH(CH₃)₂), 24.5 (OCH₂CH₂), 22.4 (CH(CH₃)₂), 5.9 (Si(CH₃)₃) ppm. ³¹P{¹H} NMR (C₆D₆, 161.9 MHz, 25 °C): δ = 40.6 ppm. Elem. anal. calcd for C₄₁H₅₈SrN₃OPSeSi₂ (862.6 g mol⁻¹): C, 57.08; H, 6.78; N, 4.87. Found: C, 56.79; H, 6.63; N, 4.71.

Ph₂P(Se)NC₆H₄CH=N–(Dipp)}Ca{N(SiMe₃)₂}(THF)] (3). Following the same procedure as that described for 2, {L³}H (0.35 g, 0.64 mmol), KN(SiMe₃)₂ (0.26 g, 1.28 mmol) and CaI₂ (0.19 g, 0.64 mmol) were reacted in THF (20 + 20 mL) to afford the title compound as a pale yellow solid. Yield (0.37 g, 71%). Light yellow crystals of 2 suitable for single-crystal X-ray crystallography were obtained by storage of a concentrated pentane solution at −30 °C. ¹H NMR (C₆D₆, 500.1 MHz, 298 K): δ = 8.06 (dd, ³J_HH = 12.8 Hz, ⁴J_HH = 7.7 Hz, 4H; PC₆H₅), 7.92 (s, 1H; CH=N), 7.13 (overlapping m, 3H; NC₆H₃, PC₆H₅), 7.02 (complex m, 5H; PC₆H₅ and C₆H₄), 6.94 (d, ³J_HH = 7.9 Hz, 2H; NC₆H₃), 6.86 (d, ³J_HH = 7.7 Hz, 1H; C₆H₄), 6.73 (t, ³J_HH = 7.3 Hz, 1H; C₆H₄), 6.46 (t, ³J_HH = 7.3 Hz, 1H; C₆H₄), 3.43 (br s, 4H; OCH₂CH₂), 3.23 (sept, ³J_HH = 8 Hz, 2H; CH(CH₃)₂), 1.29 (d, ³J_HH = 6.6 Hz, 6H; CH(CH₃)₂), 1.09 (br s, 4H; OCH₂CH₂), 0.95 (d, ³J_HH = 6.5 Hz, 6H; CH(CH₃)₂), 0.37 (s, 18H, Si(CH₃)₃) ppm. ¹³C{¹H} NMR (C₆D₆, 125.76 MHz, 298 K): δ = 171.5 (CH=N), 152.2 (i-N=CHC₆H₄), 152.1 (i-NC₆H₃), 149.6 (i-PC₆H₅), 139.5 (o-NC₆H₃), 135.8 (o-NC₆H₃), 132.7 (o-PC₆H₅), 131.8 (p-PC₆H₅), 130.6 (C₆H₄), 128.0 (p-PC₆H₅), 127.9 (p-NC₆H₃), 126.7 (m-NC₆H₃), 126.5 (m-PC₆H₅), 125.7 (m-PC₆H₅), 123.9 (m-PC₆H₅), 123.7 (C₆H₄), 123.4 (NC₆H₄), 118.5 (C₆H₄), 68.7 (OCH₂CH₂), 28.3 (CH(CH₃)₂), 25.4 (CH(CH₃)₂), 24.5 (OCH₂CH₂), 22.4 (CH(CH₃)₂), 5.9 (Si(CH₃)₃) ppm. ³¹P{¹H} NMR (C₆D₆, 161.9 MHz, 298 K): δ = 31.1 (¹J_PSe = 589 Hz) ppm. ⁷⁷Se{¹H} NMR (C₆D₆, 76.31 MHz, 298 K): δ = −61.0 (d, ¹J_SeP = 589 Hz) ppm. Elem. anal. calcd for C₄₁H₅₈CaN₃OPSeSi₂ (815.1 g mol⁻¹): C, 60.41; H, 7.17; N, 5.16. Found: C, 59.99, H, 7.03; N, 4.93.

[Ca{Ph₂P(S)NC₆H₄CH=N–(Dipp)}₂] (5). Following the same procedure as that described for 2, {L²}H (0.3 g, 0.60 mmol), KN(SiMe₃)₂ (0.12 g, 0.60 mmol) and CaI₂ (88 mg, 0.30 mmol) were reacted in THF (20 + 20 mL) to afford the title compound as a pale yellow solid. Yield (0.208 g, 67%). Light yellow crystals of 5 suitable for single-crystal X-ray crystallography were obtained by storage of a concentrated ether solution at −30 °C. ¹H NMR (C₆D₆, 400 MHz, 298 K): δ = 8.13 (m, 8H; PC₆H₅), 7.88 (s, 2H; CH=N), 7.25 (m, 6H; NC₆H₃, PC₆H₅), 7.06 (m, 10H; PC₆H₅ and C₆H₄), 6.99 (m, 4H, NC₆H₃), 6.89 (d, ³J_HH = 7.8 Hz, 2H; C₆H₄), 6.78 (t, ³J_HH = 7.4 Hz, 2H; C₆H₄), 6.48 (t, ³J_HH = 7.6 Hz, 2H; C₆H₄), 2.89 (sept, ³J_HH = 8 Hz, 4H; CH(CH₃)₂), 1.07 (d, ³J_HH = 6.8 Hz, 24H; CH(CH₃)₂), ¹³C{¹H} NMR (C₆D₆, 100 MHz, 298 K): δ = 171.2 (CH=N), 152.5 (i-N=CHC₆H₄), 152.2 (i-NC₆H₃), 149.1 (i-PC₆H₅), 139.6 (o-NC₆H₃), 135.1 (o-NC₆H₃), 132.8 (o-PC₆H₅), 131.7 (p-PC₆H₅), 130.3 (C₆H₄), 128.0 (p-PC₆H₅), 127.8 (p-NC₆H₃), 126.9 (m-NC₆H₃), 126.4 (m-PC₆H₅), 125.9 (m-PC₆H₅), 123.5 (m-PC₆H₅), 123.4 (C₆H₄), 123.1 (NC₆H₄), 118.5 (C₆H₄), 28.2 (CH(CH₃)₂), 25.2 (CH(CH₃)₂), 22.1 (CH(CH₃)₂) ppm. ³¹P{¹H} NMR (C₆D₆, 161.9 MHz, 298 K): δ = 62.6 ppm Elem. anal. calcd for for C₆₂H₆₄CaN₄P₂S₂ (1030.4 g mol⁻¹): C, 72.20; H, 6.25; N, 5.43 Found: C, 59.99, H, 7.03; N, 4.93.

Typical protocol for intermolecular hydroelementation reactions

In the glovebox, the precatalyst (10 μL) was loaded into an NMR tube. The NMR tube was stored in an appropriate Schlenk tube, which was then removed from the glove-box to allow manipulations on a double manifold Schlenk line. The subsequent manipulations were performed using standard Schlenk techniques. Styrene (58 μL 500 μmol) and diphenylphosphine or pyrrolidine (500 μmol) were added to the NMR tube using microsyringes. The NMR tube was sealed and shaken vigorously, then put into an oil bath at desire temperature. The reaction times were measured from this point. After the required amount of time, the reaction was quenched by adding C₆D₆ to the mixture at room temperature. The conversion was determined according to the ¹H NMR spectrum of the reaction mixture.

X-ray crystallographic analyses

Single crystals of complex {L³}H were obtained from a concentrated solution of toluene at room temperature while single crystals of complexes 3 and 5 were obtained from saturated solution of pentane and diethylether respectively under argon atmosphere at a temperature of −35 °C. In each case, a crystal of suitable dimensions was mounted on a CryoLoop (Hampton Research Corp.) with a layer of light mineral oil and placed in a nitrogen stream at 150(2) K. All measurements were made either on an Agilent Supernova X-calibur Eos CCD detector with either graphite-monochromatic Cu-Kα (1.54184 Å, for L³H and 5) or Bruker-AXS, APEXII CCD detector with Mo-Kα (0.71073 Å for 3) radiation. Crystal data and structure refinement parameters are summarised in Table TS1 in ESI.† The structures were solved by direct methods (SIR2004) (ref. 20) and refined on F² using the full-matrix least-squares method, using SHELXL-97.²¹ Non-hydrogen atoms were anisotropically refined. H-atoms were included in the refinement on calculated positions riding on their carrier atoms. The function minimised was [∑w(F_o² − F_c²)²] (w = 1/[σ²(F_o²) + (aP)² + bP]), where P = (Max(F_o²,0) + 2F_c²)/3 with σ²(F_o²) from counting statistics. The function R₁ and wR₂ were (∑||F_o| − |F_c||)/∑|F_o| and [∑w(F_o² − F_c²)²/∑(wF_o⁴)]^1/2 respectively. The DIAMOND-3 program was used to draw the molecule. Crystallographic data (excluding structure factors) for the structures reported in this article have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC 1479903 (L³H), 1479904 (3) and 1479905 (5).

Acknowledgements

This work was supported by Science and Engineering Research Board (SERB), Department of Science and Technology (DST), India under project no. SB/S1/IC/045/2013. S. A. thanks CSIR for his PhD fellowship, and the Science and Technology Department, Embassy of France in India, Bangalore, for travel grants towards his research stay in Rennes.

Notes and references

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Footnote

† Electronic supplementary information (ESI) available: X-ray crystallographic files for {L³}H, 3 and 5 in CIF format, Table TS1 and the spectral data of new compounds, representation of the solid-state structure of 4. CCDC 1479903–1479905. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c6ra13117d

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