Synthesis and properties of anionic ruthenium thionitrosyl and selenonitrosyl complexes that contain tetraanionic 2-hydroxybenzamidobenzene ligands

Abstract

Although transition-metal complexes that contain thiocarbonyl (CS) and selenocarbonyl (CSe) ligands have been well studied, only three neutral or cationic selenonitrosyl (NSe) complexes have been reported, while anionic NSe complexes remain elusive. Herein, we report the first examples of anionic NSe-ligated ruthenium complexes, which were obtained from the reaction of anionic ruthenium nitrido complexes, elemental selenium, and 4-(N,N-dimethylamino)pyridine (DMAP). The structures of one of these ruthenium NSe complexes, as well as of the corresponding thionitrosyl (NS) and nitrosyl (NO) complexes, were systematically examined by X-ray diffraction analyses and theoretical calculations. In contrast to previous reportes, the NSe ligand in these complexes is a better π-acceptor than the NO and NS ligands and exhibits a stronger trans influence.

---

Introduction

The chemistry of nitric oxide (NO) is well investigated, primarily due to the importance of NO in a biological context, e.g. in cell signalling and other physiological functions in living organisms.¹ Accordingly, it is hardly surprising that numerous transition-metal complexes of NO have been studied in depth.² Yet, the chemistry of the heavier isologues of NO, i.e., nitric sulfide (NS) and nitric selenide (NSe), has attracted less attention, as these species can only be detected in harsh environments such as low-temperature matrixes.³ Stabilizing these fleeting species in transition-metal complexes would afford an opportunity to study the properties of these thionitrosyl (M–NS) and selenonitrosyl complexes (M–NSe) and thus broaden our understanding of the chemistry of NS and NSe.

In contrast to the chemistry of thiocarbonyl (CS) and selenocarbonyl (CSe) transition-metal complexes,⁴ that of NS and NSe complexes has been much less developed, which is probably due to the scarcity of NS and NSe complexes. The first transition-metal complexes of NS was obtained from the reaction of a molybdenum nitrido complex with elemental sulfur,⁵ and other NS complexes have also been prepared by the treatment of the corresponding transition-metal nitrido complexes⁶ with elemental sulfur⁷ or its equivalents.^8,9 Moreover, reactions of metal complexes with trithiazyl chloride (N₃S₃Cl₃) as the NS source have been reported.¹⁰ Following the successful synthesis of NS complexes from the corresponding nitrido complexes, a few NSe complexes were prepared by the reaction of nitrido complexes with elemental selenium,^7a,c,d albeit that this approach is less generic for NSe than for NS. For example, cis-[Ru(N)(Cl)L₂] (L = 2-[(2,6-diisopropylphenyl)imino]methyl-4,6-dibromophenolato), did not afford the corresponding NSe complex under reaction conditions similar to those for the reaction with NS.^7e

To investigate the properties of the chalcogenonitrosyls (NE; E = O, S, Se) in transition-metal complexes, systematic studies on a series of NE complexes would be highly desirable.¹¹ So far, only three series of NE complexes have been reported, which include neutral and cationic metal complexes of [Os(NE)Cl₂Tp] (Tp = hydrotris(1-pyrazolyl)borate),^7a [Ru(NE)Cl₃(AsPh₃)₂]^7d,12 and [Ir(NE){N(CHCHP^tBu₂)₂}][PF₆]^7c,13 (Fig. 1). Conversely, a series of anionic transition-metal NE complexes has not yet been reported. Examples of anionic NS complexes remain scarce,¹⁴ while anionic NSe complexes remain elusive. The synthesis of such a series of anionic NE (E = O, S, Se) complexes should thus be important to gain deeper insight into the chemistry of NE, particularly with respect to the question how the overall charge influence the properties of such NE complexes. Herein, we report the synthesis of anionic ruthenium NE (E = O, S, Se) complexes that bear tetraanionic 2-hydroxybenzamidobenzene ligands, i.e., [Ph₄P][Ru(NE)(hybeb^R1,R2)(dmap)] (E = O, S, Se; hybeb = N,N′-(1,2-phenylene)bis(2-hydroxybenzamide), R¹ = H, Cl; R² = H, Cl, CF₃; dmap = 4-(N,N-dimethylamino)pyridine). The structures of some of these NE complexes were determined in detail by a combination of single-crystal X-ray diffraction analyses and theoretical calculations. All the Ru–NE complexes obtained in this study are classified as {RuNE}⁶ according to the Enemark-Feltham notation.¹⁵

Fig. 1 Examples of a series of transition-metal NE (E = O, S, Se) complexes.

Results and discussion

Syntheses of 2-hydroxybenzamidobenzene derivatives (H₄hybeb^R1,R2)

We selected the 2-hydroxybenzamidobenzene derivatives H₄hybeb^R1,R2 (1) as tetradentate ligands for the synthesis of anionic NE complexes of ruthenium, as they can be readily prepared, and offer an opportunity to study the electronic effect on the properties of the complexes. Moreover, when such ligands coordinate to transition metals, a rigid structure is usually formed. Unsubstituted H₄hybeb^H,H (1a) was prepared in 92% yield by the Ph₃PCl₂-mediated condensation¹⁶ of salicylic acid and 1,2-phenylenediamine (Scheme 1), and substituted H₄hybeb^H,Cl (1b) and H₄hybeb^Cl,Cl (1c) were prepared in good yield under similar reaction conditions.

Scheme 1 Synthesis of H₄hybeb^R1,R2 ligands 1a–c.

Unexpectedly, the attempted synthesis of H₄hybeb derivatives with a CF₃ group at R² [1d: H₄hybeb^H,CF₃; 1e: H₄hybeb^Cl,CF₃] failed under the conditions shown in Scheme 1. To prepare these compounds, we treated THP-protected 4-(trifluoromethyl)phenol with BuLi and ethyl chloroformate to afford ester 2 (Scheme 2).¹⁷ Subsequently, 2 was treated with 1,2-phenylenediamine derivatives in the presence of sodium bis(trimethylsilyl)amide (NaHMDS)¹⁸ to furnish the corresponding THP-protected H₄hybeb^R1,CF₃. Finally, the THP group was removed under acidic conditions to generate 1d and 1e in good yield. The H₄hybeb^R1,R2 ligands 1a–e contained a small amount of solvent molecules (hexane or EtOAc) that could not be removed (Fig. S1–S4 and S7–S10, ESI†).

Scheme 2 Synthesis of H₄hybeb^R1,CF₃ ligands 1d and 1e.

Syntheses of the nitrido complexes [Ph₄P][Ru(N)(hybeb^R1,R2)] (3)

With H₄hybeb^R1,R2 ligands 1a–e in hand, we focused on the preparation of nitrido complexes that bear tetraanionic hybeb^R1,R2 ligands as precursors for the synthesis of the corresponding NS and NSe complexes. Based on a modified literature procedure (Scheme 3),^19a the reaction of 1a and [Bu₄N][Ru(N)Cl₄]²⁰ in the presence of an excess 2,6-lutidine in a mixture of MeOH/THF (3 : 1, v/v) afforded the tetrabutylammonium salt [Bu₄N][Ru(N)(hybeb^H,H)],¹⁹ which was treated with [Ph₄P]Br to afford nitrido complex [Ph₄P][Ru(N)(hybeb^H,H)] (3a) in 72% yield. The cation metathesis was necessary to obtain single crystals suitable for an X-ray diffraction analysis. Nitrido complexes 3b–e were prepared in a similar fashion and obtained as orange/red crystals, which are air- and moisture-stable in both the solid state and in solution.

Scheme 3 Synthesis of nitrido complexes 3.

The molecular structure of nitrido complex [Ph₄P][Ru(N)(hybeb^H,CF₃)] (3d) was unambiguously determined by a single-crystal X-ray diffraction analysis. Complex 3d exhibits a distorted square-pyramidal coordination geometry in which the nitride ligand is located at the apical position (Fig. 2). Based on this analysis, the ruthenium center in 3 exhibits a 16-electron configuration with the formal oxidation state of +6. The length of the Ru1–N1 bond in 3d (1.6040(15) Å) falls in the range of previously reported five-coordinate anionic ruthenium nitrido complexes such as [Na(dme)][Ru(N)(meso-octamethylporphyrinogen)] (1.569(6) Å (ref. 21)), [Bu₄N][Ru(N)(hybeb^H,H)] (1.594(4) Å (ref. 19a)), [Bu₄N][Ru(N)(O₂C₆H₄)₂] (1.603(4) Å (ref. 22)), and [Bu₄N][Ru(N)(S₂C₆H₄)₂] (1.613(5) Å (ref. 23)).

Fig. 2 Molecular structure of the anionic part of nitrido complex 3d. Hydrogen atoms are omitted for clarity and only selected atoms are labelled. Selected bond length (Å): Ru1–N1 1.6040(15).

Syntheses of the NS complexes [Ph₄P][Ru(NS)(hybeb^R1,R2)(dmap)] (4)

Subsequently, we synthesized NS complexes via the reaction of 3 with elemental sulfur (Table 1). When 3a was treated at room temperature with 1/8 S₈ (10 equiv.) in the presence of DMAP (10 equiv.), the colour of the mixture gradually turned from orange to black. The reaction reached completion after 40 h, and the NS complex [Ph₄P][Ru(NS)(hybeb^H,H)(dmap)] (4a) was isolated in 67% yield in the form of black plates (entry 1). An acceleration of the reaction progress was observed when nitrido complexes with electron-withdrawing groups on the hybeb ligands were used (entries 2 and 3). After 0.5–1.5 h, the reactions of 3b and 3c with sulfur and DMAP smoothly furnished good yields of 4b and 4c, respectively. The reactivity of CF₃-substituted complexes 3d and 3e was very high, and the reactions were complete after 15 min (entries 4 and 5). The formation of NS complexes was not observed when the reaction was carried out in the absence of DMAP.

Table 1 Syntheses of NS complexes 4a–e

Entry	3	R^1	R^2	Time (h)	Product	Yield (%)
1	3a	H	H	40	4a	67
2	3b	H	Cl	1.5	4b	72
3	3c	Cl	Cl	0.5	4c	73
4	3d	H	CF3	0.25	4d	74
5	3e	Cl	CF3	0.25	4e	69

---

Two possible pathways can be considered for the formation of these NS complexes. A sulfurization of the nitrido complexes would most likely result in the formation of unisolable intermediates of the type [Ph₄P][Ru(NS)(hybeb^R1,R2)],^14e followed by coordination of DMAP to stabilize these unsaturated complexes, which would lead to the coordinatively saturated product 4. Alternatively, the reactivity of the nitrido ligand in 3 would be increased upon coordination of DMAP trans to the nitrido ligand prior to the formation of the nitrogen–sulfur bond.^6d In order to examine the pathway and the role of DMAP toward the formation of 4, we monitored the reactions of 3 with (a) sulfur in the absence of DMAP, and with (b) DMAP in the absence of sulfur by ¹H NMR spectroscopy. However, changes were not observed in these ¹H NMR spectra: the mechanism of this reaction and the role of DMAP remains unclear at this stage.

The molecular structure of 4d was unequivocally determined by a single-crystal X-ray diffraction analysis (Fig. 3). The six-coordinate octahedral geometry of the ruthenium center was confirmed, whereby the DMAP ligand is located trans to the NS ligand. The Ru–N–S angle is 171.0(3)/172.2(3)°, which confirms a terminal coordination and linear alignment of the NS ligand. The N–S bond length in 4d [1.511(4)/1.516(6)] is similar to those in other NS complexes such as mer-[Ru(NS)Cl₃(AsPh₃)₂] (1.502(4) Å (ref. 7d)), [Ph₄P][Ru(NS)Cl₄(H₂O)] (1.504(4) Å (ref. 14a)), [Ph₄P][Os(NS)Cl₄(H₂O)] (1.514(5) Å (ref. 14b)), and [(Ir(NS){N(CHCHP^tBu₂)₂}][PF₆] (1.522(2) Å (ref. 7c)).

Fig. 3 Molecular structure of the anionic part of NS complex 4d. Only one of the two independent anions per unit cell is shown. Hydrogen atoms are omitted for clarity and only selected atoms are labelled. Selected bond lengths (Å) and angles (°): S1–N1 1.511(4); N1–Ru1 1.746(4); Ru1–N2 2.155(4); S1–N1–Ru1 171.0(3); N1–Ru1–N2 173.53(19).

Syntheses of the NSe complexes [Ph₄P][Ru(NSe)(hybeb^R1,R2)(dmap)] (5)

Next, we attempted to synthesize NSe complexes via a similar approach, using elemental selenium instead of sulfur (Table 2). As expected, in accordance with the aforementioned low reactivity of 3a and 3b, the corresponding NSe complexes [Ph₄P][Ru(NSe)(hybeb^R1,R2)(dmap)] (5a: R¹ = R² = H; 5b: R¹ = H, R² = Cl) were not formed (entries 1 and 2). The reaction of 3c with selenium and DMAP proceeded sluggishly and led only to the formation of an equilibrium mixture between 3c and the product [Ph₄P][Ru(NSe)(hybeb^Cl,Cl)(dmap)] (5c) in a ratio of 60 : 40 after 36 h. From the mixture, 5c could be isolated in 38% yield in the form of black microcrystals (entry 3). Considering the electrophilic nature of the nitrido ligand in high-valent ruthenium complexes,²⁴ we anticipated that hybeb^R1,CF₃ ligands with a CF₃ group should enhance the reactivity of the nitrido complexes. In fact, when 3d and 3e were treated with selenium in the presence of DMAP, full conversion of 3d and 3e was observed after 12 h. The corresponding anionic ruthenium NSe complexes [Ph₄P][Ru(NSe)(hybeb^H,CF₃)(dmap)] (5d) and [Ph₄P][Ru(NSe)(hybeb^Cl,CF₃)(dmap)] (5e) were obtained in 46% and 48% yields, respectively (entries 4 and 5), and these represent the first examples of anionic transition-metal NSe complexes.

Table 2 Syntheses of NSe complexes 5c–e

Entry	3	R^1	R^2	Time (h)	Product	Yield (%)
1	3a	H	H	72	5a	0
2	3b	H	Cl	72	5b	0
3	3c	Cl	Cl	36	5c	38
4	3d	H	CF3	12	5d	46
5	3e	Cl	CF3	12	5e	48

---

NSe complexes 5c–e are stable in the solid state under air and at low temperature in solution. However, 5c–e decompose in solution at room temperature, even under an atmosphere of argon. When a CDCl₃ solution of 5d was kept standing at room temperature (Scheme 4), the gradual liberation of DMAP under concomitant formation of nitrido complex 3d and a black precipitate (presumably elemental selenium) was observed. The addition of DMAP (10 equiv.) or selenium (10 equiv.) to the CDCl₃ solution inhibited the decomposition, and only ca. 40% of 5d was converted into 3d after 24 h. An intermediate was not observed in the ¹H NMR spectrum of the reaction mixture. Due to the instability of the NSe complexes, it was necessary to work up the reaction rapidly, and the recrystallization had to be conducted at low temperature.

Scheme 4 Decomposition of NSe complex 5d in CDCl₃ into nitrido complex 3d.

The molecular structure of 5d was determined by crystallographic measurements (Fig. 4). Structural features similar to those of NS complex 4d were observed for NSe complex 5d, which exhibits a six-coordinate octahedral coordination geometry with a linear Ru–N–Se linkage [171.2(3)/169.9(3)°] and short Ru–NSe and N–Se distances. The N–Se bond distance in 5d [1.670(4)/1.671(4) Å] is longer than those in [Os(NSe)Cl₂Tp] (1.629(10) Å (ref. 7a)) and mer-[Ru(NSe)Cl₃(AsPh₃)₂] (1.650(3) Å (ref. 7d)), but similar to that in [(Ir(NSe){N(CHCHP^tBu₂)₂}][PF₆] (1.678(4) Å (ref. 7c)).

Fig. 4 Molecular structure of the anionic part of NSe complex 5d. Only one of the two independent anions per unit cell is shown. Hydrogen atoms are omitted for clarity and only selected atoms are labelled. Selected bond lengths (Å) and angles (°): Se1–N1 1.670(4); N1–Ru1 1.734(4); Ru1–N2 2.173(4); Se1–N1–Ru1 171.2(3); N1–Ru1–N2 173.79(16).

Encouraged by the successful synthesis of these NSe complexes, we further studied the synthesis of hitherto unprecedented tellurium analogues of NO complexes, i.e., telluronitrosyl (NTe) complexes. However, all attempts to synthesize NTe complexes via the reaction of 3 and elemental tellurium in the presence of pyridines failed, which might be attributed to the low solubility of elemental tellurium in common organic solvents. It should be noted here that this result is consistent with previously reported results on the reactions of osmium and neutral ruthenium nitrido complexes.^7a,d

Synthesis of the NO complex [Ph₄P][Ru(NO)(hybeb^H,CF₃)(dmap)] (6)

To compare the structures of NS complex 4d and NSe complex 5d with the corresponding NO complex [Ph₄P][Ru(NO)(hybeb^H,CF₃)(dmap)] (6), we attempted to synthesize 6via the oxidation of 3d using Me₃NO,^7a,e,13 H₂O₂ ²⁵ or O₂ with Et₃B·DMAP,^4e but all of these attempts were unsuccessful. Therefore, 6 was synthesized according to a modified literature method (Scheme 5):²⁶1d was treated with sodium hydride, followed by [RuNOCl₃]²⁶ and DMAP to generate the sodium salt Na[Ru(NO)(hybeb^H,CF₃)(dmap)]. A subsequent cation metathesis with [Ph₄P]Br afforded the targeted NO complex 6 in the form of black crystals (34% yield over two steps).

Scheme 5 Synthesis of NO complex 6.

In its IR spectrum, NO complex 6 exhibits a ν(NO) absorption at 1810 cm⁻¹, while the ν(NS) and the ν(NSe) bands of 4d and 5d, respectively could not be clearly identified due to the overlap with vibrational stretches arising from the hybeb^R1,R2 ligand and the [Ph₄P]⁺ ion. The molecular structure of 6 was determined by a single-crystal X-ray diffraction analysis (Fig. 5). The alignment of the Ru–N–O moiety is almost linear [174.9(2)/177.27(19)°] with an N–O bond distance of 1.144(3)/1.149(3) Å, which is similar to that in other NO complexes such as mer-[Ru(NO)Cl₃(AsPh₃)₂] (1.151(9) Å (ref. 12)) and [(Ir(NO){N(CHCHP^tBu₂)₂}][PF₆] (1.168(3) Å (ref. 7c)), but shorter than that in [Os(NO)Cl₂Tp] (1.19(4) Å (ref. 7a)).

Fig. 5 Molecular structure of the anionic part of NO complex 6. Only one of the two independent anions per unit cell is shown. Hydrogen atoms are omitted for clarity and only selected atoms are labelled. Selected bond lengths (Å) and angles (°): O1–N1 1.144(3); N1–Ru1 1.752(2); Ru1–N2 2.1325(19); O1–N1–Ru1 174.9(2); N1–Ru1–N2 176.57(8).

Properties of a series of NE complexes

The selected metric parameters, Wiberg bond indices (WBI) and the natural population analysis (NPA) charge distributions for a series of the obtained NE complexes (E = O, 6; E = S, 4d; E = Se, 5d) are summarized in Table 3 together with those of nitrido complex 3d for comparison. The Ru–NE bond lengths in 6, 4d, and 5d are longer compared to the Ru–N bond length in 3d [Ru–N (3d): 1.6040(15) Å; Ru–NO (6): 1.75 Å (mean); Ru–NS (4d): 1.75 Å (mean); Ru–NSe (5d): 1.73 Å (mean)]. The WBIs of the Ru–NE bonds in 6, 4d, and 5d decrease compared to the Ru–N bond in 3d. Considering the previously reported WBI for nitrido complex [(Ir(N){N(CHCHP^tBu₂)₂}][PF₆]¹³ and iridium NE complexes [(Ir(NE){N(CHCHP^tBu₂)₂}][PF₆],^7c,12 the Ru–N triple bond in 3d should turn into a double bond after the nitrido ligand bonds with chalcogen atoms to generate 4d and 5d.

Table 3 Selected bond lengths (Å),^a angles (°),^a WBIs^b and NPA charges^b for nitrido complex 3d and NE complexes 6 (E = O), 4d (E = S), 5d (E = Se)

E	Nothing (3d)	O (6)	S (4d)	Se (5d)
a Distances and bond angles of both molecules per unit cell are shown. b The calculation of WBIs and NPA charges were performed at the B3PW91/SBKJC(d) level of theory.
Bond angles
dmap–Ru–N	—	176.57(8)	173.53(19)	173.79(16)
		176.82(8)	173.78(19)	172.78(17)
Ru–N–E	—	174.9(2)	171.0(3)	171.2(3)
		177.27(19)	172.2(3)	169.9(3)
Bond lengths
RuN–E	—	1.144(3)	1.511(4)	1.670(4)
		1.149(3)	1.516(4)	1.671(4)
Ru–NE	1.6040(15)	1.752(2)	1.746(4)	1.734(4)
		1.744(2)	1.746(4)	1.732(4)
N(dmap)–Ru	—	2.1325(19)	2.155(4)	2.173(4)
		2.1327(18)	2.157(4)	2.173(4)
Wiberg bond index
RuN–E	—	1.8352	1.6889	1.5792
Ru–NE	2.3049	1.4144	1.3629	1.4072
N(dmap)–Ru	—	0.3154	0.2881	0.2753
NPA charges
Ru	1.111	0.883	0.980	1.006
N (NE)	−0.065	0.401	−0.348	−0.409
E	—	−0.224	0.370	0.390

---

The Ru–NE bond lengths are comparable to the sum of the covalent double-bond radii (Ru=N: 1.74 Å),²⁷ and the WBIs corroborate double-bond character for the Ru–NE bonds in the NE complexes (Ru–NO: 1.4144; Ru–NS: 1.3629; Ru–NSe: 1.4072). The N–E bond lengths [N–O: 1.15 Å (mean); N–S: 1.51 Å (mean); N–Se: 1.67 Å (mean)] are longer than the calculated covalent triple-bond radii (N≡O: 1.07 Å; N≡S: 1.49 Å; N≡Se: 1.61 Å),²⁷ but similar to the corresponding double-bond radii (N=O: 1.17 Å; N=S: 1.54 Å; N=Se: 1.67 Å).²⁷ Taking the WBIs into account (N–O: 1.8352; N–S: 1.6889; N–Se: 1.5792), the N–E bonds in 4d, 5d, and 6 exhibit double-bond character.

The obtained data revealed characteristic features of the NE ligands, i.e., the order of π-back donation and trans influence of the NE ligands. The length of the Ru–NSe bond in 5d slightly decreases compared to the corresponding Ru–NO and Ru–NS bonds in 6 and 4d [Ru–NO (6): 1.75 Å (mean); Ru–NS (4d): 1.75 Å (mean); Ru–NSe (5d): 1.73 Å (mean)]. This result could be explained in terms of an increased π-back donation from the ruthenium center to the NSe ligand, which appears to reflect a better π-accepting character of the NSe ligand relative to the lighter chalcogen homologues. This trend is consistent with previously reported estimations based on theoretical calculations.²⁸ However, it should also be noted here that this trend contradicts previous studies on complexes such as [Cr(NS)(OH₂)₅]²⁺,²⁹ [Os(NE)Cl₂Tp]^7a or [Ru(NE)Cl₃(AsPh₃)₂],^7d,12 in which the respective NO ligands appear to be better π-acceptors than the NS and NSe ligands, as well as the studies on [Ir(NE){N(CHCHP^tBu₂)₂}][PF₆],^7c,13 where the π-acceptor ability of the NS ligand is lower than that of the NO and NSe ligands.³⁰

The aforementioned π-accepting nature of the NSe ligand in 5d was corroborated by the NPA charge distribution on the RuNSe moiety. The positive charge on the ruthenium atom is greater in 5d than in 6 and 4d [RuNO (6): 0.883; RuNS (4d): 0.980; RuNSe (5d): 1.006], while the negative charge on the nitrogen atom of the NE ligand is greater in 5d than in 6 and 4d [RuNO (6): 0.401; RuNS (4d): −0.348; RuNSe (5d): −0.409]. Therefore, the NSe ligand appears to be a better π-acceptor than the NO and NS ligands.

The NSe ligand in 5d exhibits a stronger trans influence than the NO and NS ligands in 6 and 4d, respectively. The N(dmap)–RuNE bond length slightly increases in the order E = O < S < Se [N–RuNO (6): 2.13 Å (mean); N–RuNS (4d): 2.16 Å (mean); N–RuNSe (5d): 2.17 Å (mean)], and the corresponding WBIs of N(dmap)–Ru decrease in the same order [N–RuNO (6): 0.3154; N–RuNS (4d): 0.2880; N–RuNSe (5d): 0.2753]. Considering the order of trans influence, the NSe ligand appears to exhibit a better σ-donating ability than the lighter chalcogen homologues. This trend is consistent with the data obtained for [Ru(NE)Cl₃(AsPh₃)₂] (E = O, S, Se)^7d,12 wherein the NS and NSe ligands exert a stronger trans influence than the NO ligand.

Conclusions

Anionic ruthenium NS and NSe complexes were synthesized via the reaction of the corresponding nitrido complexes with elemental sulfur or selenium in the presence of DMAP, which provided the first anionic NSe complexes. The structural properties of these NE (E = O, S, Se) complexes were determined by single-crystal X-ray diffraction analyses and theoretical calculations, which revealed that in these complexes, the NSe ligand is the best π-acceptor with the strongest trans influence.

Experimental

General considerations

Unless otherwise noted, all reactions were performed in oven-dried (110 °C) glassware under an atmosphere of dry argon (balloon). Reagents were obtained from common commercial sources and used as received. Anhydrous solvents for reactions were purchased from Kanto Chemical Co., Inc. and used as received. Solvents for workup, column chromatography, and recrystallization were of ‘reagent grade’. The following compounds were prepared as described in the literature: [Bu₄N][Ru(N)Cl₄],²⁰ tetrahydro-2-[4-(trifluoromethyl)phenoxy]-2H-pyran,¹⁷ and [Ru(NO)Cl₃].²⁶ Commercially available sulfur powder was recrystallized from benzene prior to use. TLC was performed on Merck TLC silica gel 60 F₂₅₄ plates. Silica gel used for flash column chromatography (silica gel 60N; spherical; neutral; 40–50 μm) was obtained from Kanto Chemical Co., Inc. Alumina used for column chromatography (Aluminium Oxide 90; active neutral; 63–200 μm) was obtained from Merck.

Melting points are uncorrected. IR spectra were recorded using a diamond-attenuated total reflectance (ATR) unit and are corrected. NMR spectra were recorded at ambient temperature on a JEOL ECZ 400 spectrometer (¹H: 400 MHz; ¹³C: 100 MHz; ¹⁹F: 375 MHz; ³¹P: 161 MHz). Chemical shifts are reported in δ, relative to residual ¹H and ¹³C{¹H} signals of CDCl₃ (¹H: δ 7.24; ¹³C{¹H}: 77.16) and (CD₃)₂SO with 0.03% v/v TMS (¹H: δ 2.50; ¹³C{¹H}: δ 39.52) or to the external ¹⁹F signal of C₆F₆ (δ −164.9) or ³¹P{¹H} signal of H₃PO₄ (δ 0.00). ESI-HRMS were obtained on an FT-ICR mass spectrometer. Elemental analyses were performed on a Perkin-Elmer 2400 series II CHN analyser. The number of solvent molecules in the products was determined by elemental analysis and ¹H NMR spectroscopy.

General procedure for the syntheses of N,N′-(1,2-phenylene)bis(2-hydroxybenzamide) and derivatives (1a–c)

A previous reported procedure was slightly modified.¹⁵ Ph₃PCl₂ (4.8 equiv.) was added to a CHCl₃ (40 mL) solution of phenylenediamine (1.0 equiv.) and salicylic acid (2.4 equiv.), and the mixture was stirred under reflux for 17 h. The resulting mixture was poured into iced water and extracted with EtOAc. The organic layer was consecutively treated with an aqueous solution of HCl (4 M), a saturated aqueous solution of NaHCO₃, and brine. The organic layer was dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo. The residue was passed through silica gel (EtOAc) in order to remove Ph₃PO, and the fraction R_f ≈ 0.8 was collected and concentrated in vacuo. The residual material was purified by column chromatography on silica gel (EtOAc/hexane) to afford the product as a white solid.

N,N′-(1,2-Phenylene)bis(2-hydroxybenzamide)·0.1EtOAc (1a·0.1EtOAc). 1,2-Phenylenediamine (0.324 g, 3.00 mmol), salicylic acid (0.994 g, 7.20 mmol), and Ph₃PCl₂ (4.66 g, 14.0 mmol) were used as reagents. EtOAc/hexane = 1 : 1 was used as the eluent after Ph₃PO was removed. 1a·0.1EtOAc was isolated as a white solid (0.981 g, 2.75 mmol, 92% yield). The NMR data of synthesized 1a was consistent with reported data.³¹

N,N′-(1,2-Phenylene)bis(5-chloro-2-hydroxybenzamide)·0.1EtOAc (1b·0.1EtOAc). 1,2-Phenylenediamine (0.324 g, 3.00 mmol), 5-chlorosalicylic acid (1.24 g, 7.20 mmol) and Ph₃PCl₂ (4.66 g, 14.0 mmol) were used as reagents. EtOAc/hexane = 1 : 1 was used as the eluent after Ph₃PO was removed. 1b·0.1EtOAc was isolated as a white solid (1.14 g, 2.68 mmol, 89% yield). The ¹H NMR data matched those reported previously.³²¹³C{¹H} NMR ((CD₃)₂SO with 0.03% v/v TMS): δ 170.4 (EtOAc), 164.9, 157.0, 133.4, 131.0, 129.1, 126.0, 125.5, 123.1, 119.3, 118.7, 59.8 (EtOAc), 20.8 (EtOAc), 14.1 (EtOAc). HRMS (ESI−) m/z: [M − H]⁻ calcd for C₂₀H₁₃N₂O₄³⁵Cl₂: 415.0255; found: 415.0258. IR (ATR, cm⁻¹): ν_NH = 3311, ν_CO = 1645. mp: 248.6–251.4 °C.

N,N′-(4,5-Dichloro-1,2-phenylene)bis(5-chloro-2-hydroxybenzamide)·0.1EtOAc (1c·0.1EtOAc). 4,5-Dichlro-1,2-phenylenediamine (0.531 g, 3.00 mmol), 5-chlorosalicylic acid (1.24 g, 7.20 mmol) and Ph₃PCl₂ (4.66 g, 14.0 mmol) were used as reagents. EtOAc/hexane = 1 : 3 was used as the eluent after Ph₃PO was removed. 1c·0.1EtOAc was isolated as white solid (1.24 g, 2.51 mmol, 84% yield). ¹H NMR ((CD₃)₂SO with 0.03% v/v TMS): δ 11.81 (s, 2H), 10.53 (s, 2H), 8.16 (s, 2H), 7.99 (d, J = 2.6 Hz, 2H), 7.49 (dd, J = 8.8, 2.7 Hz, 2H), 7.03 (d, J = 8.9 Hz, 2H), 4.02 (q, J = 7.1, 0.2H, EtOAc), 1.98 (s, 0.3H, EtOAc), 1.17 (t, J = 7.1 Hz, 0.3H, EtOAc). ¹³C{¹H} NMR ((CD₃)₂SO with 0.03% v/v TMS): δ 164.6, 156.6, 133.6, 131.0, 129.3, 127.4, 126.2, 123.2, 119.2, 118.6. HRMS (ESI−) m/z: [M − H]⁻ calcd for C₂₀H₁₁N₂O₄³⁵Cl₄: 482.9477; found 482.9478. IR (ATR, cm⁻¹): ν_NH = 3332, ν_CO = 1636. mp: 284.7–286.7 °C.

Synthesis of ethyl 2-((tetrahydro-2H-pyran-2-yl)oxy)-5-(trifluoromethyl)benzoate (2). A previously reported procedure was slightly modified for the preparation of 2.¹⁶ BuLi (1.55 M solution in hexane, 0.79 mL, 1.22 mmol, 1.1 equiv.) was added dropwise to a THF (6.7 mL) solution of tetrahydro-2-[4-(trifluoromethyl)phenoxy]-2H-pyran¹⁶ (0.273 g, 1.11 mmol, 1.0 equiv.) at −78 °C, where the mixture was stirred for 1 h. The mixture was then transferred into a −78 °C solution of ethyl chloroformate (0.132 g, 1.22 mmol, 1.1 equiv.) in THF (1.9 mL), allowed to warm to room temperature, where it was stirred for 2 h. The resulting mixture was added into water and extracted with EtOAc. The organic layer was treated with water and brine, dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo. The residue was purified by column chromatography on silica gel (EtOAc/hexane = 1 : 10, v/v) to afford 2 as a colourless oil (0.251 g, 0.789 mmol, 71% yield). ¹H NMR (CDCl₃): δ 8.02 (d, J = 2.3 Hz, 1H), 7.63 (dd, J = 8.9, 2.5 Hz, 1H), 7.29 (d, J = 8.7 Hz, 1H), 5.58 (t, J = 2.7 Hz, 1H), 4.36 (qd, J = 7.1, 1.9 Hz, 2H), 3.83 (dd, J = 11.2, 3.0 Hz, 1H), 3.60 (d, J = 11.0 Hz, 1H), 1.61–2.04 (m, 6H), 1.37 (t, J = 7.1 Hz, 3H). ¹³C{¹H} NMR (CDCl₃): δ 165.5, 158.7, 130.0 (dd, J = 3.9, 2.9 Hz), 128.8 (q, J = 3.9 Hz), 124.0 (q, J = 271.7 Hz), 123.2 (q, J = 33.7 Hz), 121.8, 116.2, 96.6, 61.9, 61.4, 30.1, 25.2, 18.1, 14.4. ¹⁹F NMR (CDCl₃): δ −60.3. HRMS (ESI+) m/z: [M + Na]⁺ calcd for C₁₅H₁₇O₄F₃Na⁺: 341.0974; found 341.0971. IR (ATR, cm⁻¹): ν_CO = 1732.

General procedure for the syntheses of N,N′-(1,2-phenylene)bis(5-trifluoromethyl-2-hydroxybenzamide) derivatives 1d and 1e

A previous reported procedure was slightly modified.^18a NaHMDS (1.0 M solution in hexane, 2.0 equiv.) was added dropwise to a THF (2.0 mL) solution of 2 (1.0 equiv.) and phenylenediamine (0.45 equiv.) at 0 °C. The mixture was stirred for 5 min at 0 °C before it was allowed to warm to room temperature, where it was stirred for 16 h. The resulting mixture was added to a saturated aqueous solution of NH₄Cl and extracted with EtOAc. The organic layer was treated with water and brine, dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo to leave a red residue.

This residue was dissolved in THF (1.0 mL) and 2 M HCl (1.9 mL, 2.2 equiv.) was added. The mixture was stirred at room temperature for 8 h. The resulting mixture was added to a saturated aqueous solution of NaHCO₃ and extracted with EtOAc. The organic layer was treated with water and brine, dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo. The residue was purified by column chromatography (EtOAc/hexane) to afford the product.

N,N′-(1,2-Phenylene)bis(5-trifluoromethyl-2-hydroxybenzamide)·0.2EtOAc (1d·0.2EtOAc). 2 (0.541 g, 1.70 mmol) and 1,2-phenylenediamine (0.0827 g, 0.765 mmol) were used as reagents. EtOAc/hexane = 1 : 1 was used as the eluent. 1d·0.2EtOAc was isolated as a pale yellow solid (0.258 g, 0.514 mmol, 69% yield over 2 steps). ¹H NMR ((CD₃)₂SO with 0.03% v/v TMS): δ 12.41 (s, 2H), 10.52 (s, 2H), 8.32 (s, 2H), 7.76–7.82 (m, 4H), 7.32 (q, J = 3.2, 2H), 7.16 (d, J = 8.7 Hz, 2H), 4.03 (q, J = 7.1, 0.4H, EtOAc), 1.99 (s, 0.6H, EtOAc), 1.17 (t, J = 7.1 Hz, 0.6H, EtOAc). ¹³C{¹H} NMR ((CD₃)₂SO with 0.03% v/v TMS): δ 170.4 (EtOAc), 164.9, 161.1, 131.0, 130.4, 127.5, 126.1, 125.6, 124.3 (q, J = 271.7 Hz), 120.1 (q, J = 32.8 Hz), 118.3, 117.8, 59.8 (EtOAc), 20.7 (EtOAc), 14.1 (EtOAc). ¹⁹F NMR ((CD₃)₂SO with 0.03% v/v TMS): δ −58.4. HRMS (ESI−) m/z: [M − H]⁻ calcd for C₂₂H₁₃N₂O₄F₆: 483.0779, found 483.0785. IR (ATR, cm⁻¹): ν_NH = 3324, ν_CO = 1615. mp: 234.2–237.0 °C.

N,N′-(4,5-Dichloro-1,2-phenylene)bis(5-trifluoromethyl-2-hydroxybenzamide)·0.1EtOAc (1e·0.1EtOAc). 2 (0.541 g, 1.70 mmol) and 4,5-dichloro-1,2-phenylenediamine (0.135 g, 0.765 mmol) were used as reagents. EtOAc/hexane = 1 : 3 was used as the eluent. 1e·0.1EtOAc was isolated as pale yellow solid (0.284 g, 0.505 mmol, 66% yield over 2 steps). ¹H NMR ((CD₃)₂SO with 0.03% v/v TMS): δ 12.33 (s, 2H), 10.59 (s, 2H), 8.29 (s, 2H) 8.16 (s, 2H), 7.79 (d, J = 8.7, 2.3 Hz, 2H), 7.17 (d, J = 8.2 Hz, 2H), 4.03 (q, J = 7.1 Hz, 0.2H, EtOAc), 1.99 (s, 0.3H, EtOAc), 1.17 (t, J = 7.1 Hz, 0.3H, EtOAc). ¹³C{¹H} NMR ((CD₃)₂SO with 0.03% v/v TMS): δ 171.1 (EtOAc), 164.6, 160.7, 131.1, 130.6, 127.6, 127.5, 126.4, 124.3 (q, J = 270.7 Hz), 120.1 (q, J = 32.8 Hz), 118.3, 117.8, 59.8 (EtOAc), 20.8 (EtOAc), 14.1 (EtOAc). ¹⁹F NMR ((CD₃)₂SO with 0.03% v/v TMS): δ −58.4. HRMS (ESI−) m/z: [M − H]⁻ calcd for C₂₂H₁₁N₂O₄F₆³⁵Cl₂: 551.0008, found 551.0006. IR (ATR, cm⁻¹): ν_NH = 3357, ν_CO = 1647. mp: 274.6–277.5 °C.

General procedure for the syntheses of nitrido complexes [Ph₄P][RuN(hybeb^R1,R2)] (3)

Nitrido complexes 3 were synthesized according to a modified literature procedure.^19a 2,6-Lutidine (excess, 0.73 mL) was added to a MeOH/THF = 3 : 1 (5.1 mL : 1.7 mL) solution of 1 (0.500 mmol, 1.00 equiv.) and [Bu₄N][Ru(N)Cl₄]¹⁹ (0.250 g, 0.500 mmol, 1.0 equiv.), and the mixture was stirred for 16 h at room temperature. The solvent was removed in vacuo, and the black/brown residue was purified by column chromatography on alumina (CHCl₃). The orange band was collected and concentrated in vacuo, and the residue was recrystallized from CH₂Cl₂/hexane to afford [Bu₄N][Ru(N)(hybeb^H,H)] as an orange solid. The orange complex (1.0 equiv.) was dissolved in CH₂Cl₂ (10.0 mL per mmol) and [Ph₄P]Br (1.0 equiv.) was added. After stirring for 8 h, water was added, and the mixture was extracted with CH₂Cl₂. The organic layer was dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo. The residue was purified by column chromatography on alumina (CHCl₃) and recrystallized (CH₂Cl₂/hexane) to afford the product.

[Ph₄P][RuN(hybeb^H,H)]·0.1CH₂Cl₂ (3a·0.1CH₂Cl₂). The tetrabutylammonium salt was synthesized from 1a·0.1EtOAc (0.179 g, 0.500 mmol) in the first step. [Ph₄P]Br (0.164 g, 0.391 mmol) was used in the second step. The product was isolated as red crystals (0.291 g, 0.360 mmol, 72% yield from 1a·0.1EtOAc). ¹H NMR (CDCl₃): δ 8.91 (td, J = 6.5, 3.2 Hz, 2H), 8.21 (dd, J = 8.2, 1.8 Hz, 2H), 7.66 (td, J = 7.5, 1.1 Hz, 4H), 7.51 (td, J = 8.0, 3.7 Hz, 8H), 7.27–7.35 (m, 10H), 7.19 (dd, J = 8.2, 0.9 Hz, 2H), 6.84–6.92 (m, 4H), 5.31 (s, 0.2H, CH₂Cl₂). ¹³C{¹H} NMR (CDCl₃): δ 169.2, 166.9, 146.0, 135.5, 134.2 (d, J = 10.6 Hz), 131.8, 131.7, 130.5 (d, J = 12.5 Hz), 124.7, 122.2, 121.8, 120.0, 118.5, 117.3 (d, J = 89.6 Hz). ³¹P{¹H} NMR (CDCl₃): δ 23.5. Anal. calcd for C_44.1H_32.2Cl_0.2N₃O₄PRu (3a·0.1CH₂Cl₂): C, 65.61; H, 4.02; N, 5.21. Found: C, 65.41; H, 3.94; N, 5.19.

[Ph₄P][RuN(hybeb^H,Cl)] (3b). The tetrabutylammonium salt was synthesized from 1b·0.1EtOAc (0.213 g, 0.500 mmol) in the first step. [Ph₄P]Br (0.152 g, 0.363 mmol) was used in the second step. The product was isolated as red crystals (0.333 g, 0.384 mmol, 77% yield from 1b·0.1EtOAc). ¹H NMR (CDCl₃): δ 8.83 (td, J = 6.6, 3.0 Hz, 2H), 8.08 (d, J = 2.7 Hz, 2H), 7.64–7.68 (m, 4H), 7.50 (td, J = 7.8, 3.7 Hz, 8H), 7.34 (dd, J = 13.0, 8.0 Hz, 8H), 7.16 (dd, J = 8.9, 2.5 Hz, 2H), 7.09 (d, J = 8.7 Hz, 2H), 6.88 (td, J = 6.6, 3.0 Hz, 2H). ¹³C{¹H} NMR (CDCl₃): δ 167.9, 165.4, 145.7, 135.6 (d, J = 2.9 Hz), 134.2 (d, J = 9.6 Hz), 131.6, 130.9, 130.5 (d, J = 12.5 Hz), 125.7, 123.2, 122.6, 121.8, 121.6, 117.7, 116.8. ³¹P{¹H} NMR (CDCl₃): δ 23.7. Anal. calcd for C₄₄H₃₀Cl₂N₃O₄PRu (3b): C, 60.91; H, 3.49; N, 4.84. Found: C, 60.79; H, 3.24; N, 4.83.

[Ph₄P][RuN(hybeb^Cl,Cl)] (3c). The tetrabutylammonium salt was synthesized from 1c·0.1EtOAc (0.247 g, 0.500 mmol) in the first step. [Ph₄P]Br (0.162 g, 0.386 mmol) was used in the second step. The product was isolated as red crystals (0.344 g, 0.367 mmol, 73% yield from 1c·0.1EtOAc). ¹H NMR (CDCl₃): δ 9.07 (s, 2H), 8.04 (d, J = 2.7 Hz, 2H), 7.69 (dd, J = 8.2, 6.8 Hz, 4H), 7.53 (td, J = 7.8, 3.5 Hz, 8H), 7.38 (dd, J = 13.0, 7.5 Hz, 8H), 7.17 (dd, J = 8.7, 2.7 Hz, 2H), 7.09 (d, J = 8.7 Hz, 2H). ¹³C{¹H} NMR (CDCl₃): δ 167.7, 165.3, 145.1, 135.5 (d, J = 2.9 Hz), 134.2 (d, J = 10.6), 132.0, 130.7, 130.4 (d, J = 13.5), 124.9, 124.6, 123.4, 122.0, 121.6, 117.6, 116.7. ³¹P{¹H} NMR (CDCl₃): δ 23.7. Anal. calcd for C₄₄H₂₈Cl₄N₃O₄PRu (3c): C, 55.50; H, 2.98; N, 4.49. Found: C, 55.85; H, 2.66; N, 4.29.

[Ph₄P][RuN(hybeb^H,CF₃)] (3d). The tetrabutylammonium salt was synthesized from 1d·0.2EtOAc (0.251 g, 0.500 mmol) in the first step. [Ph₄P]Br (0.164 g, 0.391 mmol) was used in the second step. The product was isolated as red crystals (0.330 g, 0.353 mmol, 71% yield from 1d·0.2EtOAc). ¹H NMR (CDCl₃): δ 8.91 (td, J = 6.6, 3.5 Hz, 2H), 8.52 (d, J = 2.3 Hz, 2H), 7.69–7.73 (m, 4H), 7.50–7.58 (m, 10H), 7.37–7.42 (m, 8H), 7.29 (d, J = 9.1 Hz, 2H), 6.95 (td, J = 6.6, 3.5 Hz, 2H). ¹³C{¹H} NMR (CDCl₃): δ 169.1, 168.0, 145.6, 135.7 (d, J = 2.9 Hz), 134.2 (d, J = 9.6 Hz), 130.6 (d, J = 12.5 Hz), 130.0 (d, J = 3.9 Hz), 125.0 (q, J = 270.7 Hz), 128.4 (d, J = 2.9 Hz), 124.5, 122.8, 121.8, 120.6 (q, J = 32.8 Hz), 120.9, 117.7, 116.9. ¹⁹F NMR (CDCl₃): δ −59.3. ³¹P{¹H} NMR (CDCl₃): δ 23.7. Anal. calcd for C₄₄H₃₀Cl₄N₃O₄PRu (3d): C, 59.10; H, 3.23; N, 4.50. Found: C, 59.47; H, 2.99; N, 4.50.

[Ph₄P][RuN(hybeb^Cl,CF₃)] (3e). The tetrabutylammonium salt was synthesized from 1e·0.1EtOAc (0.281 g, 0.500 mmol) in the first step. [Ph₄P]Br (0.164 g, 0.391 mmol) was used in the second step. The product was isolated as red crystals (0.370 g, 0.369 mmol, 74% yield from 1e·0.1EtOAc). ¹H NMR (CDCl₃): δ 9.12 (s, 2H), 8.47 (d, J = 1.8 Hz, 2H), 7.73–7.77 (m, 4H), 7.59 (td, J = 7.8, 3.5 Hz, 8H), 7.54 (dd, J = 8.9, 2.1 Hz, 2H), 7.41–7.47 (m, 8H), 7.30 (d, J = 8.7 Hz, 2H). ¹³C{¹H} NMR (CDCl₃): δ 169.1, 168.0, 145.1, 135.8 (d, J = 2.9 Hz), 134.2 (d, J = 9.6 Hz), 130.6 (d, J = 12.5 Hz), 129.9 (d, J = 3.9 Hz), 128.8 (d, J = 2.9 Hz), 125.1, 124.8 (q, J = 271.7 Hz), 123.8, 122.3, 121.1, 121.0 (q, J = 32.8 Hz), 117.8, 116.9. ¹⁹F NMR (CDCl₃): δ −59.4. ³¹P{¹H} NMR (CDCl₃): δ 23.8. Anal. calcd for C₂₂H₁₂Cl₂F₆N₂O₄ (3e): C, 55.05; H, 2.81; N, 4.19. Found: C, 55.29; H, 2.47; N, 4.10.

General procedure for the syntheses of NS complexes [Ph₄P][Ru(NS)(hybeb^R1,R2)(dmap)] (4)

1/8 S₈ (0.160 g, 5.00 mmol, 10 equiv. as S) and DMAP (0.611 g, 5.00 mmol, 10 equiv.) were added to a MeCN solution (20 mL) of nitrido complex 3 (0.500 mmol, 1.0 equiv.). After the mixture was stirred at room temperature for the reaction time shown in Table 1, the solvent was removed in vacuo. The residue was dissolved in a small amount of acetone, and a large amount of water was added. The resulting brown solid was collected by filtration and recrystallized from acetone/MTBE (methyl tert-butyl ether) to afford 4 as black crystals.

[Ph₄P][Ru(NS)(hybeb^H,H)(dmap)] (4a). 3a·0.1CH₂Cl₂ (0.404 g, 0.500 mmol) was used. The reaction was completed after 40 h. The product was isolated as black crystals (0.320 g, 0.336 mmol, 67% yield). ¹H NMR (CDCl₃): δ 8.98 (td, J = 6.6, 3.0 Hz, 2H), 8.26 (dd, J = 8.2, 1.8 Hz, 2H), 7.75–7.78 (m, 6H), 7.62 (td, J = 8.0, 3.7 Hz, 8H), 7.39–7.44 (m, 8H), 7.07 (dd, J = 8.2, 1.4 Hz, 2H), 6.97–7.01 (m, 2H), 6.65 (td, J = 6.6, 3.0 Hz, 2H), 6.45–6.49 (m, 2H), 5.91 (d, J = 6.4 Hz, 2H), 2.68 (s, 6H). ¹³C{¹H} NMR (CDCl₃): δ 169.2, 168.3, 154.3, 147.8, 146.6, 135.9 (d, J = 2.9 Hz), 134.4 (d, J = 10.6 Hz), 133.3, 130.9 (d, J = 13.49 Hz), 124.8, 122.6, 122.4, 121.4, 117.4 (d, J = 89.6 Hz), 114.9, 105.9, 39.0. ³¹P{¹H} NMR (CDCl₃): δ 32.6. HRMS (ESI−) m/z: [M − Ph₄P − dmap]⁻ calcd for C₂₀H₁₂N₃O₄RuS: 491.9592; found 491.9604.

[Ph₄P][Ru(NS)(hybeb^H,Cl)(dmap)] (4b). 3b (0.434 g, 0.500 mmol) was used. The reaction was completed in 1.5 h. The product was isolated as black crystals (0.368 g, 0.360 mmol, 72% yield). ¹H NMR (CDCl₃): δ 8.92 (dd, J = 5.7, 3.9 Hz, 2H), 8.12 (s, 2H), 7.75 (t, J = 7.3 Hz, 4H), 7.66 (d, J = 6.4 Hz, 2H), 7.60 (td, J = 7.2, 3.3 Hz, 8H), 7.46 (d, J = 8.7 Hz, 2H), 6.85 (d, J = 8.7 Hz, 2H), 6.69 (q, J = 3.2 Hz, 2H), 5.84 (s, 2H), 2.60 (s, 6H). ¹³C{¹H} NMR (CDCl₃): δ 167.8, 167.0, 154.3, 147.6, 146.3, 135.8 (d, J = 1.9 Hz), 134.4 (d, J = 10.6 Hz), 132.2, 130.8 (d, J = 13.5), 130.4, 125.6, 123.7, 122.5, 121.6, 119.1, 117.4 (d, J = 89.6 Hz), 105.7, 38.8. ³¹P{¹H} NMR (CDCl₃): δ 23.6. Anal. calcd for C₅₁H₄₀Cl₂N₅O₄PRuS (4b): C, 59.54; H, 3.95; N, 6.85. Found: C, 59.73; H, 3.77; N, 6.61.

[Ph₄P][Ru(NS)(hybeb^Cl,Cl)(dmap)]·0.5MTBE (4c·0.5MTBE). 3c (0.468 g, 0.500 mmol) was used. The reaction was completed in 30 min. The product was isolated as black crystals (0.414 g, 0.365 mmol, 73% yield). ¹H NMR (CDCl₃): δ 9.22 (s, 2H), 8.13 (d, J = 2.7 Hz, 2H), 7.76–7.80 (m, 4H), 7.60–7.65 (m, 10H), 7.48–7.53 (m, 8H), 7.01 (d, J = 8.7 Hz, 2H), 6.92 (dd, J = 8.9, 3.0 Hz, 2H), 5.93 (d, J = 7.1 Hz, 2H), 3.18 (s, 1.5H, MTBE), 2.69 (s, 6H), 1.16 (s, 4.5H, MTBE). ¹³C{¹H} NMR (CDCl₃): δ 167.9, 167.2, 154.5, 147.6, 145.8, 135.9 (d, J = 3.1 Hz), 134.4 (d, J = 9.6 Hz), 132.1, 130.8 (d, J = 12.5 Hz), 125.0, 123.9, 123.6, 122.7, 119.5, 117.5 (d, J = 89.6 Hz), 105.9, 72.8 (MTBE), 49.6 (MTBE), 39.0, 27.1 (MTBE). ³¹P{¹H} NMR (CDCl₃): δ 23.8. Anal. calcd for C_53.5H₄₄Cl₄N₅O_4.5PRuS (4c·0.5MTBE): C, 56.62; H, 4.00; N, 6.48. Found: C, 56.26; H, 3.77; N, 6.08.

[Ph₄P][Ru(NS)(hybeb^H,CF₃)(dmap)] (4d). 3d (0.467 g, 0.500 mmol) was used. The reaction was completed in 15 min. The product was isolated as black crystals (0.402 g, 0.369 mmol, 74% yield). ¹H NMR (CDCl₃): δ 8.96 (q, J = 3.3 Hz, 2H), 8.55 (s, 2H), 7.77 (dd, J = 8.2, 6.4 Hz, 4H), 7.70 (d, J = 6.8 Hz, 2H), 7.61 (td, J = 8.0, 3.7 Hz, 8H), 7.44–7.49 (m, 8H), 7.23 (d, J = 10.5 Hz, 4H), 7.14 (d, J = 8.7 Hz, 2H), 6.74 (td, J = 6.6, 3.0 Hz, 2H), 5.95 (s, 2H), 2.72 (s, 6H). ¹³C{¹H} NMR (CDCl₃): δ 171.5, 167.1, 154.5, 147.6, 146.4, 135.9 (d, J = 2.9 Hz), 134.4 (d, J = 10.6 Hz), 131.5 (d, J = 3.9 Hz), 130.8 (d, J = 13.5 Hz), 127.2 (d, J = 2.9 Hz), 125.7 (q, J = 270.7 Hz), 124.1, 122.9, 122.7, 121.8, 117.4 (d, J = 89.6 Hz), 116.3 (q, J = 31.8 Hz), 105.9, 39.0. ¹⁹F NMR (CDCl₃): δ −60.0. ³¹P{¹H} NMR (CDCl₃): δ 23.7. Anal. calcd for C₅₃H₄₀F₆N₅O₄PRuS (4d): C, 58.53; H, 3.78; N, 6.38. Found: C, 58.72; H, 3.59; N, 6.23.

[Ph₄P][Ru(NS)(hybeb^Cl,CF₃)(dmap)] (4e). 3e (0.502 g, 0.500 mmol) was used. The reaction was completed in 15 min. The product was isolated as black crystals (0.402 g, 0.347 mmol, 69% yield). ¹H NMR (CDCl₃): δ 9.25 (s, 2H), 8.53 (d, J = 2.3 Hz, 2H), 7.79 (dd, J = 8.2, 6.8 Hz, 4H), 7.60–7.65 (m, 10H), 7.51 (dd, J = 12.8, 7.3 Hz, 8H), 7.28 (dd, J = 8.7, 2.3 Hz, 2H), 7.14 (d, J = 8.7 Hz, 2H), 5.98 (d, J = 7.3 Hz, 2H), 2.74 (s, 6H). ¹³C NMR (CDCl₃): δ 171.4, 167.3, 154.6, 147.5, 145.8, 136.0 (d, J = 2.9 Hz), 134.5 (d, J = 9.6 Hz), 131.4 (d, J = 3.9 Hz), 130.9 (d, J = 2.9 Hz), 127.5, 125.6 (q, J = 270.7 Hz), 123.8, 123.5, 123.2, 117.5 (d, J = 89.6 Hz), 116.8 (q, J = 31.8 Hz), 106.0, 39.1. ¹⁹F NMR (CDCl₃): δ −58.7. ³¹P NMR (CDCl₃): δ 23.8. Anal. calcd for C₅₁H₃₈Cl₂F₆N₅O₄PRuS (4e): C, 54.98; H, 3.31; N, 6.05. Found: C, 55.25; H, 3.46; N, 5.96.

General procedure for the syntheses of NSe complexes [Ph₄P][Ru(NSe)(hybeb^R1,R2)(dmap)] (5)

A 30 mL two-necked flask containing grey selenium powder (0.790 g, 10.0 mmol, 20 equiv.) was heated under vacuum, before argon gas was introduced. In a separate flask, nitrido complex 3 (0.500 mmol, 1.0 equiv.) and DMAP (0.611 g, 5.00 mmol, 10 equiv.) were dissolved in MTBE/CH₂Cl₂ (15 mL : 1 mL) at room temperature. The resulting solution was added to the flask containing the dried selenium, and the mixture was stirred at room temperature for the reaction time shown in Table 2. The solvent was removed in vacuo to leave a black residue. During the subsequent manipulations, the temperature of the solution containing the product should be kept below 0 °C. To remove the selenium powder, the residue was suspended at 0 °C in CH₂Cl₂ and filtered through a pad of Celite into a glass tube that was kept at 0 °C. The filtrate was layered with MTBE and stored in a refrigerator (0 °C) for one day to afford 5 as black crystals, which were collected by suction filtration or decantation, and dried under vacuum.

During the measurements of the ¹³C{¹H} NMR spectra, 5c–e decomposed to generate nitrido complexes 3c–e, DMAP, and selenium. For this reason, the ¹³C{¹H} NMR spectra exhibit signals of 5c–e together with those of 3c and DMAP (Fig. S32, S34, and S36, ESI†).

[Ph₄P][Ru(NSe)(hybeb^Cl,Cl)(dmap)]·0.5MTBE (5c·0.5MTBE). 3c (0.468 g, 0.500 mmol) was used. The reaction reached completion within 72 h. 5c·0.5MTBE was isolated as black crystals (0.222 g, 0.188 mmol, 38% yield). ¹H NMR (CDCl₃): δ 9.19 (d, J = 0.91, 2H), 8.14 (q, J = 1.4 Hz, 2H), 7.80 (dd, J = 7.8, 5.9 Hz, 4H), 7.64 (td, J = 7.8, 3.7 Hz, 8H), 7.58 (d, J = 5.9 Hz, 2H), 7.49–7.54 (m, 8H), 7.01 (dd, J = 8.7, 2.7 Hz, 2H), 6.95 (td, J = 5.8, 2.9 Hz, 2H), 5.98 (dd, J = 6.6, 5.2 Hz, 2H), 3.19 (s, 3H, MTBE), 2.74 (s, 6H), 1.16 (s, 9H, MTBE). ¹³C{¹H} NMR (CDCl₃): δ 167.7, 167.1, 154.6, 147.5, 145.7, 135.9 (d, J = 2.9 Hz), 134.4 (d, J = 10.6 Hz), 132.1, 130.8 (d, J = 12.5 Hz), 125.1, 124.2, 124.1, 123.7, 122.9, 120.0, 118.0, 117.5 (d, J = 89.6 Hz), 106.0, 72.9 (MTBE), 49.6 (MTBE), 39.1, 27.1 (MTBE). ³¹P{¹H} NMR (CDCl₃): δ 23.8. Anal. calc. for C_51.5H_39.2Cl₄N₅O_4.1PRuSe (5c·0.5MTBE): C, 53.95; H, 3.45; N, 6.11. Found: C, 53.69; H, 3.41; N, 5.93.

[Ph₄P][Ru(NSe)(hybeb^H,CF₃)(dmap)]·0.5MTBE (5d·0.5MTBE). 3d (0.467 g, 0.500 mmol) was used. The reaction reached completion within 36 h. 5d·0.5MTBE was isolated as black crystals (0.270 g, 0.229 mmol, 46% yield). ¹H NMR (CDCl₃): δ 8.91 (td, J = 6.6, 3.2 Hz, 2H), 8.53 (d, J = 2.3 Hz, 2H), 7.76–7.80 (m, 4H), 7.66 (dd, J = 6.0, 1.4 Hz, 2H), 7.60–7.63 (m, 8H), 7.45–7.50 (m, 8H), 7.22 (d, J = 2.3 Hz, 2H), 7.14 (d, J = 8.6 Hz, 2H), 6.71 (td, J = 6.6, 3.2 Hz, 2H), 5.96 (dd, J = 6.0, 1.4 Hz, 2H), 3.19 (s, 1.5H, MTBE), 2.73 (s, 6H), 1.17 (s, 4.5H, MTBE). ¹³C{¹H} NMR (CDCl₃): δ 171.2, 167.1, 154.5, 147.5, 146.3, 135.8 (d, J = 1.9 Hz), 134.4 (d, J = 9.6 Hz), 131.4 (d, J = 4.8 Hz), 130.8 (d, J = 13.5 Hz), 127.2 (d, J = 2.9 Hz), 125.7 (q, J = 270.7 Hz), 124.2, 123.1, 122.8, 121.9, 117.5 (d, J = 89.6 Hz), 116.6 (q, J = 31.8 Hz), 105.97, 72.93 (MTBE), 49.60 (MTBE), 39.01, 27.12 (MTBE). ¹⁹F NMR (CDCl₃): δ −58.5. ³¹P{¹H} NMR (CDCl₃): δ 23.7. Anal. calc. for C_55.5H₄₆F₆N₅O_4.5PRuSe (5d·0.5MTBE): C, 56.49; H, 3.93; N, 6.10. Found: C, 56.07; H, 3.83; N, 5.89.

[Ph₄P][Ru(NSe)(hybeb^Cl,CF₃)(dmap)]·0.6MTBE (5e·0.6MTBE). 3e (0.502 g, 0.500 mmol) was used. The reaction reached completion within 36 h. 5e·0.6MTBE was isolated as black crystals (0.304 g, 0.242 mmol, 48% yield). ¹H NMR (CDCl₃): δ 9.22 (d, J = 1.4 Hz, 2H), 8.53 (s, 2H), 7.80 (t, J = 7.5 Hz, 4H), 7.59–7.65 (m, 10H), 7.52 (dd, J = 13.0 Hz, 8.4 Hz, 8H), 7.29 (d, J = 8.7 Hz, 2H), 7.18 (d, J = 8.7 Hz, 2H), 6.00 (d, J = 6.4 Hz, 2H), 3.19 (s, 1.8H, MTBE), 2.77 (s, 6H), 1.17 (s, 5.4H, MTBE). ¹³C{¹H} NMR (CDCl₃): δ 171.3, 167.3, 154.6, 147.4, 145.7, 135.9 (d, J = 2.9 Hz), 134.4 (d, J = 9.6 Hz), 131.3 (d, J = 2.9 Hz), 130.8 (d, J = 9.6 Hz), 127.5 (d, J = 2.9 Hz), 125.6 (q, J = 270.7 Hz), 123.9, 123.6, 123.3, 122.9, 117.5 (d, J = 89.6 Hz), 116.9 (q, J = 32.8 Hz), 106.0, 72.9 (MTBE), 49.6 (MTBE), 39.1, 27.1 (MTBE). ¹⁹F NMR (CDCl₃): δ −58.4. ³¹P{¹H} NMR (CDCl₃): δ 23.8. Anal. calc. for C₅₆H_45.2Cl₂F₆N₅O_4.6PRuSe (5e·0.6MTBE): C, 53.38; H, 3.55; N, 5.61. Found: C, 53.28; H, 3.53; N, 5.45.

Synthesis of NO complex [Ph₄P][Ru(NO)(hybeb^H,CF₃)(dmap)] (6)

Initially, a previously reported procedure was modified.²⁵ A solution of 1d·0.1EtOAc (0.178 g, 0.360 mmol, 1.0 equiv.) in DMF (12 mL) was added to NaH, and the mixture was stirred for 0.5 h. The colour of the mixture changed from yellow to brown. The mixture was then transferred to a DMF (5 mL) solution of [RuNOCl₃]²⁵ (0.0855 g, 0.360 mmol, 1.0 equiv.) and DMAP (0.0440 g, 0.360 mmol, 1.0 equiv.). The mixture was stirred under reflux for 2 h, before the solvent was removed by distillation. The black residue was dissolved in acetonitrile and filtered, before the filtrate was concentrated in vacuo. The crude product was purified by recrystallization from acetone/MTBE to yield the sodium salt as a black solid.

Next, a solution of [Ph₄P]Br (0.0717 g, 0.171 mmol, 1.0 equiv.) in CH₂Cl₂ (3 mL) was added and the mixture was stirred overnight. The mixture was transferred into water and extracted with CH₂Cl₂. The organic layer was dried over anhydrous Na₂SO₄, filtered, and concentrated in vacuo. The residue was purified by column chromatography on alumina (CHCl₃/MeOH = 20 : 1, v/v) and the product was recrystallized from CH₂Cl₂/MTBE to afford 6 as black crystals (0.132 g, 0.123 mmol, 34% yield from 1d·0.1EtOAc). ¹H NMR (CDCl₃): δ 8.99 (td, J = 6.3, 2.7 Hz, 2H), 8.58 (d, J = 1.4 Hz, 2H), 7.83 (d, J = 7.3 Hz, 2H), 7.75 (dd, J = 7.9, 6.7 Hz, 4H), 7.59 (td, J = 7.8, 3.5 Hz, 8H), 7.42–7.47 (m, 8H), 7.21–7.24 (m, 2H), 7.08 (d, J = 8.7 Hz, 2H), 6.79 (q, J = 3.3 Hz, 2H), 6.00 (d, J = 6.8 Hz, 2H), 2.72 (s, 6H). ¹³C{¹H} NMR (CDCl₃): δ 170.9, 166.7, 154.7, 147.3, 145.3, 135.9 (d, J = 2.9 Hz), 134.3 (d, J = 10.6 Hz), 131.5 (d, J = 3.9 Hz), 130.8 (d, J = 13.5 Hz), 127.1 (d, J = 1.9 Hz), 125.7 (q, J = 270.7 Hz), 124.2, 122.7, 122.6, 121.7, 117.4 (d, J = 89.6 Hz), 116.3 (q, J = 32.8 Hz), 105.9, 39.0. ¹⁹F NMR (CDCl₃): δ −58.6. ³¹P{¹H} NMR (CDCl₃): δ 23.5. HRMS (ESI−) m/z: [M − Ph₄P − dmap]⁻ calcd for C₂₂H₁₀F₆N₃O₅Ru: 611.9568; found 611.9582. IR (ATR, cm⁻¹): ν_NO = 1810.

X-ray diffraction studies

All diffraction data were collected at −173 °C on a Bruker Apex II Ultra X-ray diffractometer equipped with a Mo-Kα radiation (λ = 0.71073 Å) source. Intensity data were processed using the Apex3 software suite. The solution of the structures and the corresponding refinements were carried out using the Yadokari-XG³³ graphical interface. The positions of the non-hydrogen atoms were determined by using the SHELXT³⁴ program and refined on F² by full-matrix least-squares techniques using the SHELXL-2018³⁵ program. All non-hydrogen atoms were refined with anisotropic thermal parameters, while all hydrogen atoms were placed using AFIX instructions. Details of the diffraction data are summarized in Tables S1–S4 (ESI†). For 4d and 5d, the structures were refined as an inversion twin. Although two residual peaks slightly above 1 e Å⁻³ were observed in the final difference map, these have no chemical meaning.

Computational details

All density functional theory (DFT) calculations were performed using the Gaussian 09 package.³⁶ The computers used in this study are part of the computer facilities of the Academic Center for Computing Media Studies (ACCMS) at Kyoto University (Japan). The geometries of the anionic part of 4d, 5d, and 6 were fully optimized using the B3PW91³⁷ density functional with the effective core potential (ECP) proposed by Stevens et al.,³⁸ SBKJC, with double-ζ polarization functions, which is denoted SBKJC(d) in this paper. Vibrational analyses based on force constant matrices (Hessians) were carried out at the stationary points in order to identify minima (all positive constants), transition states (one negative force constant), or higher-order saddle points. NAO-based Wiberg bond indices³⁹ and natural population analysis (NPA) charge distributions⁴⁰ were estimated using the NBO6.0 program⁴¹ based on the optimized structures. Optimized Cartesian coordinates of anionic part for 4d, 5d, and 6 are summarized in Tables S5–S7 (ESI†).

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This research was supported by JSPS KAKENHI Grant Number 23550082. We would thank Prof. Youichi Ishii (Chuo University, Japan) for his generous support as well as Mr Wataru Abe and Mr Takashi Kurihara (Chuo University, Japan) for their assistance in the early stages of this work. We would like to thank members of the Ishii Research Group for elemental analysis measurements (Chuo University, Japan), and Prof. Mao Minoura for his help on the solution of the solid-state structures. Furthermore, we would like to thank ACCMS at Kyoto University and the Research Center for Computational Science Okazaki (Japan) for providing access to their computational facilities.

Notes and references

1. (a) F. Murad, Angew. Chem., Int. Ed., 1999, 38, 1856–1868; (b) R. F. Furchgott, Angew. Chem., Int. Ed., 1999, 38, 1870–1880; (c) L. J. Ignarro, Angew. Chem., Int. Ed., 1999, 38, 1882–1892; (d) K. Ghimire, H. M. Altmann, A. C. Straub and J. S. Isenberg, Am. J. Physiol.: Cell Physiol., 2017, 312, C254–C262; (e) A. De Mel, F. Murad and A. M. Seifalian, Chem. Rev., 2011, 111, 5742–5767.
2. (a) T. W. Hayton, P. Legzdins and W. B. Sharp, Chem. Rev., 2002, 102, 935–991; (b) B. Machura, Coord. Chem. Rev., 2005, 249, 2277–2307; (c) M. J. Rose and P. K. Mascharak, Coord. Chem. Rev., 2008, 252, 2093–2114.
3. For studies on NS, see: (a) W. M. Irvine, M. Senay and A. J. Lovell, Icarus, 2000, 143, 412–414; (b) S. B. Yaghlane, S. Lahmar, Z. B. Lakhdar and M. Hochlaf, J. Phys. B: At., Mol. Opt. Phys., 2005, 38, 3395–3403; (c) S. B. Yaghlane and M. Hochlaf, J. Phys. B: At., Mol. Opt. Phys., 2009, 42, 015101. For studies on NSe, see: (d) J. M. Brown and H. Uehara, J. Chem. Phys., 1987, 87, 880–884; (e) D. H. Shi, P. L. Li, J. F. Sun and Z. L. Zhu, Spectrochim. Acta, Part A, 2014, 117, 109–119; (f) L. Andrews and P. Hassanzadeh, J. Chem. Soc., Chem. Commun., 1994, 1523–1524. For theoretical studies on NE molecules, see: (g) R. T. Boeré and T. L. Roemmele, in Comprehensive Inorganic Chemistry II, ed. J. Reedikj and K. Poeppelmeier, Elsevier, 2013, vol. 1, pp. 375–411.  DOI:10.1016/B978-0-08-097774-4.00117-0.
4. (a) W. Petz, Coord. Chem. Rev., 2008, 252, 1689–1733; (b) L. Busetto and V. Zanotti, Inorg. Chim. Acta, 2008, 361, 3004–3011; (c) Y. Mutoh, N. Kozono, K. Ikenaga and Y. Ishii, Coord. Chem. Rev., 2012, 256, 589–605; (d) A. F. Hill and C. M. A. McQueen, Organometallics, 2012, 31, 2482–2485; (e) A. Suzuki, T. Arai, K. Ikenaga, Y. Mutoh, N. Tsuchida, S. Saito and Y. Ishii, Dalton Trans., 2017, 46, 44–48; (f) I. A. Cade, A. F. Hill and C. M. A. McQueen, Dalton Trans., 2019, 48, 2000–2012; (g) B. J. Frogley, A. F. Hill and L. J. Watson, Dalton Trans., 2019, 48, 12598–12606.
5. J. Chatt and J. R. Dilworth, J. Chem. Soc., Chem. Commun., 1974, 508.
6. (a) J. F. Berry, Comments Inorg. Chem., 2009, 30, 28–66; (b) X.-Y. Yi, Y. Liang and C. Li, RSC Adv., 2013, 3, 3477–3486; (c) J. M. Smith, in Progress of Inorganic Chemistry, ed. K. D. Karlin, John Wiley & Sons, 2014, ch. 6, vol. 58, pp. 417–470; (d) W.-L. Man, W. W. Y. Lam and T.-C. Lau, Acc. Chem. Res., 2014, 47, 427–439.
7. (a) T. J. Crevier, S. Lovell and J. M. Mayer, J. Am. Chem. Soc., 1998, 120, 6607–6608; (b) B. L. Tran, R. Thompson, S. Ghosh, X. Gao, C.-H. Chen, M.-H. Baik and D. J. Mindiola, Chem. Commun., 2013, 49, 2768–2770; (c) M. G. Scheibel, I. Klopsch, H. Wolf, P. Stollberg, D. Stalke and S. Schneider, Eur. J. Inorg. Chem., 2013, 3836–3839; (d) H.-Y. Ng, W.-M. Cheung, E. K. Huang, K.-L. Wong, H. H.-Y. Sung, I. D. Williams and W. H. Leung, Dalton Trans., 2015, 44, 18459–18468; (e) H.-Y. Ng, N.-M. Lam, M. Yang, X.-Y. Yi, I. D. Williams and W.-H. Leung, Inorg. Chim. Acta, 2013, 394, 171–175.
8. For reactions with carbon disulphide, see: (a) E.-S. El-Samanody, K. D. Demadis, L. A. Gallagher, T. J. Meyer and P. S. White, Inorg. Chem., 1999, 38, 3329–3336; (b) K. D. Demadis, E.-S. El-Samanody, T. J. Meyer and P. S. White, Inorg. Chem., 1998, 37, 838–839.
9. For reactions with thiosulfate salt, see: (a) A. Wu, A. Dehestani, E. Saganic, T. J. Crevier, W. Kaminsky, D. E. Cohen and J. M. Mayer, Inorg. Chim. Acta, 2006, 359, 2842–2849; (b) X.-Y. Yi, T. C. H. Lam, Y.-K. Sau, Q.-F. Zhang, I. D. Williams and W.-H. Leung, Inorg. Chem., 2007, 46, 7193–7198.
10. (a) B. W. S. Kolthammer and P. Legzdins, J. Am. Chem. Soc., 1978, 100, 2247–2248; (b) M. Herberhold and L. Haumaier, Z. Naturforsch., B: Anorg. Chem., Org. Chem., 1980, 35, 1277–1280; (c) D. S. Bohle, C.-H. Hung, A. K. Powell, B. D. Smith and S. Wocadlo, Inorg. Chem., 1997, 36, 1992–1993.
11. For theoretical studies of NE complexes, see: (a) S. F. Vyboishchikov and G. Frenking, Theor. Chem. Acc., 1999, 102, 300–308; (b) J. W. Dethlefsen, E. D. Hedegård, R. D. Rimmer, P. C. Ford and A. Døssing, Inorg. Chem., 2009, 48, 231–238; (c) J. R. Dethlefsen, A. Døssing and E. D. Hedegård, Inorg. Chem., 2010, 49, 8769–8778; (d) A. Døssing, Coord. Chem. Rev., 2016, 306, 544–557.
12. D. H. F. Souza, G. Oliva, A. Teixeira and A. A. Batista, Polyhedron, 1995, 14, 1031–1034.
13. M. G. Scheibel, B. Askevold, F. W. Heinemann, E. J. Reijerse, B. de Bruin and S. Schneider, Nat. Chem., 2012, 4, 552–558.
14. (a) J. W. Bats, K. K. Pandey and H. W. Roesky, J. Chem. Soc., Dalton Trans., 1984, 2081–2083; (b) K. K. Pandey, H. W. Roesky, M. Noltemeyer and G. M. Sheldrick, Z. Naturforsch., B: Anorg. Chem., Org. Chem., 1984, 39, 590–593; (c) J. B. Raynor, T. J. Kemp and A. M. Thyer, Inorg. Chim. Acta, 1992, 193, 191–196; (d) U. Abram, R. Hübener, R. Wollert, R. Krimse and W. Hiller, Inorg. Chim. Acta, 1993, 206, 9–14; (e) M. Reinel, T. Höcher, U. Abram and R. Kirmse, Z. Anorg. Allg. Chem., 2003, 629, 853–861.
15. J. H. Enemark and R. D. Feltham, Coord. Chem. Rev., 1974, 13, 339–406.
16. I. Azumaya, T. Okamoto, F. Imabeppu and H. Takayanagi, Tetrahedron, 2003, 59, 2325–2331.
17. H. Geneste and B. Schäfer, Synthesis, 2001, 2259–2262.
18. (a) J. Wang, M. Rosingana, R. P. Discordia, N. Soundararajan and R. Polniaszek, Synlett, 2001, 1485–1487; (b) G. Li, C.-L. Ji, X. Hong and M. Szostak, J. Am. Chem. Soc., 2019, 141, 11161–11172.
19. (a) P.-M. Chan, W. Y. Yu, C.-M. Che and K.-K. Cheung, J. Chem. Soc., Dalton Trans., 1998, 3183–3190; (b) K.-L. Yip, W.-Y. Yu, P.-M. Chan, N.-Y. Zhu and C.-M. Che, Dalton Trans., 2003, 3556–3566.
20. W. P. Griffith and D. Pawson, J. Chem. Soc., Dalton Trans., 1973, 1315–1320.
21. L. Bonomo, E. Solari, R. Scopelliti and C. Floriani, Angew. Chem., Int. Ed., 2001, 40, 2529–2531.
22. G.-S. Fang, J.-S. Huang, N. Zhu and C.-M. Che, Eur. J. Inorg. Chem., 2004, 1341–1348.
23. D. Sellmann, M. W. Wemple, W. Donaubauer and F. Heinemann, Inorg. Chem., 1997, 36, 1397–1402.
24. R. M. Clarke and T. Storr, J. Am. Chem. Soc., 2016, 138, 15299–15302.
25. V. Panwar, A. Bansal, S. S. Ray and S. L. Jain, RSC Adv., 2016, 6, 71550–71556.
26. C. A. Johnson, S. Sharma, B. Subramaniam and A. S. Borovik, J. Am. Chem. Soc., 2005, 127, 9698–9699.
27. P. Pyykkö and M. Atsumi, Chem. – Eur. J., 2009, 15, 12770–12779.
28. (a) K. K. Pandey, M. Massoudipour and V. Paleria, Indian J. Chem., 1990, 29A, 260–262; (b) K. K. Pandey, R. B. Sharma and P. K. Pandit, Inorg. Chim. Acta, 1990, 169, 207–210; (c) K. K. Pandey, J. Coord. Chem., 1990, 22, 307–313; (d) S. F. Vyboishchikov and G. Frenking, Theor. Chem. Acc., 1999, 102, 300–308; (e) C. M. Teague, T. A. O'Brien and J. F. O'Brien, J. Coord. Chem., 2002, 55, 627–631.
29. J. W. Dethlefsen and A. Døssing, Inorg. Chim. Acta, 2009, 362, 259–262.
30. K. K. Pandey and P. Patidar, Polyhedron, 2014, 68, 87–91.
31. A. D. Keramidas, A. B. Papaioannou, A. Vlahos, T. A. Kabanos, G. Bonas, A. Makriyannis, C. P. Rapropoulou and A. Terzis, Inorg. Chem., 1996, 35, 357–367.
32. Y. A. Ibrahim and A. H. M. Elwahy, Synthesis, 1993, 503–508.
33. (a) K. Wakita, Yadokari-XG, Software for Crystal Structure Analysis, 2001; (b) C. Kabuto, S. Akine and E. Kwon, J. Crystallogr. Soc. Jpn., 2009, 51, 218–224.
34. G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2015, 71, 3–8.
35. (a) G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Crystallogr., 2008, 64, 112–122; (b) G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem., 2015, 71, 3–8; (c) J. Lübben, C. M. Wandtke, C. B. Hübschle, M. Ruf, G. M. Sheldrick and B. Dittrich, Acta Crystallogr., Sect. A: Found. Adv., 2019, 75, 50–62.
36. M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, K. Ehara, R. Toyota, J. Fukuda, M. Hasegawa, T. Ishida, Y. Nakajima, M. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery Jr., J. E. Peralta, F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin, K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox, Gaussian 09, Revision E.01, Gaussian, Inc., Wallingford, CT, 2013.
37. (a) A. D. Becke, J. Chem. Phys., 1996, 98, 5648–5652; (b) J. P. Perdew and Y. Wang, Phys. Rev. B: Condens. Matter Mater. Phys., 1992, 45, 13244–13249.
38. (a) W. J. Stevens, H. Basch and M. Krauss, J. Chem. Phys., 1984, 81, 6026–6033; (b) W. J. Stevens, M. Krauss, H. Basch and P. G. Jasien, Can. J. Chem., 1992, 70, 612–630.
39. K. B. Wiberg, Tetrahedron, 1968, 24, 1083–1096.
40. (a) J. P. Foster and F. Weinhold, J. Am. Chem. Soc., 1980, 102, 7211–7218; (b) A. E. Reed, L. A. Curtiss and F. Weinhold, Chem. Rev., 1998, 88, 899–926.
41. E. D. Glendening, J. K. Badenhoop, A. E. Reed, J. E. Carpenter, J. A. Bohmann, C. M. Morales, C. R. Landis and F. Weinhold, Theoretical Chemistry Institute, University of Wisconsin, Madison, 2013.

---

Footnote

† Electronic supplementary information (ESI) available: Copies of NMR spectra, X-ray structures and computational data of 3d, 4d, 5d and 6. CCDC 1946037–1946040. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9dt04219a

---