Preparation of chalcogenolato-bridged dinuclear Tp*Rh–Cp*Ru complexes (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate, Cp* = η⁵-pentamethylcyclopentadienyl) and binding of dioxygen to their Ru sites

Abstract

Reactions of [Tp*Rh(coe)(MeCN)] (1; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl); coe = cyclooctene) with one equiv of diphenyl dichalcogenides PhEEPh (E = Se, Te) afforded the mononuclear Rh^III complexes [Tp*Rh(EPh)₂(MeCN)] (2b: E = Se; 2c: E = Te), as reported previously for the formation of [Tp*Rh(SPh)₂(MeCN)] (2a) from the reaction of 1 and PhSSPh. Complexes 2a–2c were treated with the Ru^II complex [(Cp*Ru)₄(µ₃-Cl)₄] (Cp* = η⁵-C₅Me₅) in THF at room temperature, yielding the chalcogenolato-bridged dinuclear complexes [Tp*RhCl(µ-EPh)₂RuCp*(MeCN)] (3). Complex 3a (E = S) in solution was converted slowly into a mixture of 3a and the sterically less encumbered dinuclear complex [Tp*RhCl(SPh)(µ-η¹-S-η⁶-Ph)RuCp*] (4a) at room temperature. In 4a, one SPh group binds only to the Rh center as a terminal ligand, while the other SPh group bridges the Rh and Ru atoms by coordinating to the former at the S atom and to the latter with the Ph group in a π fashion. The Se analogue 3b also underwent a similar transformation under more forcing conditions, e.g. in benzene at reflux, whereas formation of the µ–η¹-Te-η⁶-Ph complex was not observed for the Te analogue 3c even under these forcing conditions. When complexes 3 was dissolved in THF exposed to air, the MeCN ligand bound to Ru was substituted by dioxygen to give the peroxo complexes [Tp*RhCl(µ-EPh)₂RuCp*(η²-O₂)] (5a: E = S; 5b: E = Se; 5c: E = Te). X-Ray analyses have been undertaken to determine the detailed structures for 2c, 3a, 3b, 4a, 5a, 5b, and 5c.

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Introduction

Complexes containing the hydrotris(pyrazol-1-yl)borate or its congeners with the substituted pyrazole rings as the coligand are currently attracting significant attention.¹ In a previous paper,² we reported that the reactions of Rh pyrazolylborate complexes [Tp′Rh(coe)(MeCN)] (Tp′ = Tp* (1), Tp; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl); Tp = hydrotris(pyrazol-1-yl); coe = cyclooctene) with a range of organic disulfides RSSR gave a new class of mononuclear and dinuclear Rh thiolato complexes containing Tp′ as the ancillary ligand, and from the mononuclear bis(benzenethiolato) complex [Tp*Rh(SPh)₂(MeCN)] (2a), non-symmetrical dinuclear complexes with two bridging SPh ligands [Tp*RhCl(µ-SPh)₂MCp*Cl] (M = Rh, Ir; Cp* = η⁵-C₅Me₅) can be derived by the subsequent reactions with [(Cp*MCl)₂(µ-Cl)₂]. Homo- and heterometallic dinuclear complexes obtained in this previous study represent the first chalcogenolato-bridged dinuclear complexes containing Tp′Rh units.

Now we have extended the latter reactions to that with the Ru^II complex [(Cp*RuCl)₄(µ₃-Cl)₄] and found that the analogous bimetallic complex [Tp*RhCl(µ-SPh)₂RuCp*(MeCN)] (3a) can be obtained. Interestingly, 3a in solution has proved to be converted into the singly bridged complex [Tp*RhCl(SPh)(µ–η¹-S-η⁶-Ph)RuCp*] (4a), while exposure of 3a in solution to air affords a dioxygen complex [Tp*RhCl(µ-SPh)₂RuCp*(η²-O₂)] (5a). In this paper, we wish to describe the details of 3a–5a together with the SePh and TePh analogues of 2a–5a derived similarly from 1. It is noteworthy that the selenolato and tellurolato-bridged dinuclear complexes are still limited³ and those having the Tp′Rh moiety are yet unknown.

Results and discussion

Reactions of 1 with PhEEPh (E = Se, Te)

The Rh^I complex having the Tp* ligand 1 reacted readily with one equiv of PhEEPh (E = Se, Te) in THF to give mononuclear Rh^III bis(chalcogenolato) complexes [Tp*Rh(ER)₂(MeCN)] (2b: E = Se, 2c: E = Te) (eqn (1)), as observed previously in the reaction of 1 with PhSSPh forming 2a. The reaction with PhSeSePh proceeds more smoothly than that with PhSSPh: the ¹H NMR spectra of the reaction mixture indicated that the former reaction terminated within 1 h at room temperature, whereas the latter reaction required ca. 24 h until completion under similar conditions. On the other hand, the reaction with PhTeTePh also takes place quite rapidly at room temperature but does not proceed cleanly. To avoid the formation of intractable by-products, preparation of 2c was undertaken at −20 °C.

The ¹H NMR data for 2b and 2c are in good agreement with those of 2a, indicating that these new complexes are isomorphous with the thiolato complex 2a as well as its crystallographically characterized congener [Tp*Rh(STol)₂(MeCN)] (2a′; Tol = p-MeC₆H₄). Thus, the spectra of 2b and 2c show the presence of the Tp*, EPh, and MeCN ligands in a ratio of 1 : 2 : 1, where the signals due to the 3,5-dimethylpyrazolyl groups are recorded as two sets with an intensity ratio of 2 : 1, while those ascribable to the Ph groups suggest the equivalence of the two SPh groups in solution. These features were confirmed by the X-ray analysis of 2c, whose ORTEP drawing is shown in Fig. 1. Pertinent bond distances and angles in 2c are listed in Table 1, which correspond well to those in 2a′ except for the elongation of the Rh–Te bonds by ca. 0.3 Å from the Rh–S bonds and the concomitant decrease in the E–Rh–E angle from 94.4° for E = S to 87.1° for E = Te. The difference in the Rh–E bond lengths agrees well to that of the covalent radii (Te: 1.37; S: 1.04 Å).⁴ As for the Rh–N bond distances associated with the Tp* ligand, trans influence exerted more strongly by the TePh ligand than the MeCN ligand results in the significantly longer Rh–N(2) and Rh–N(4) bonds trans to the TePh ligands at 2.163(6) and 2.151(6) Å, respectively, than the Rh–N(6) bond trans to the MeCN ligand at 2.064(7) Å.

Table 1 Selected bond distances (Å) and angles (°) in 2c

Rh–Te(1)	2.6396(7)		Rh–Te(2)	2.6486(7)
Rh–N(2)	2.163(6)		Rh–N(4)	2.151(6)
Rh–N(6)	2.064(7)		Rh–N(7)	2.005(7)
N(7)–C(28)	1.12(1)
Te(1)–Rh–Te(2)	87.06(2)	Rh–Te(1)–C(16)	105.1(2)
Rh–Te(2)–C(22)	106.9(2)	Rh–N(7)–C(28)	177.4(7)
N(7)–C(28)–C(29)	177.4(9)

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Fig. 1 An ORTEP drawing for 2c at 30% probability level. Hydrogen atoms are omitted for clarity.

For 2b, only the preliminary X-ray diffraction study was possible due to the poor quality of the crystals. Nevertheless, the similar atom-connecting scheme in the molecule has been confirmed.

Reactions of 2 with a Cp*Ru^II complex forming heterobimetallic complexes

We have reported previously that 2a reacts with 0.5 equiv of [(Cp*MCl)₂(µ-Cl)₂] (M = Rh, Cl) to give [Tp*RhCl(µ-SPh)₂MCp*Cl]. Now we have found that incorporation of the Cp*Ru^II fragment, which is isoelectronic with the above Cp*Rh^III and Cp*Ir^III moieties, occurs analogously, when 2a is allowed to react with 0.25 equiv of [(Cp*Ru)₄(µ-Cl)₄] in THF at room temperature. The product [Tp*RhCl(µ-SPh)₂RuCp*(MeCN)] (3a) in which the MeCN molecule is now bonded to the Ru site, was able to be isolated cleanly, if the product was crystallized either in a short period (< ca. 1 h) or in the presence of an excess MeCN (Scheme 1). The structure of the bimetallic core bridged by two thiolato ligands has been determined in detail by the X-ray analysis (vide infra) as shown in Fig. 2.

Fig. 2 An ORTEP drawing for 3a at 30% probability level. Hydrogen atoms are omitted for clarity. The structure and the atom numbering scheme are essentially the same for the Se analogue 3b.

Scheme 1

The ¹H NMR spectrum of 3a recorded in C₆D₆ shows only the unresolvable broad signals. However, when recorded in the presence of excess acetonitrile (e.g. C₆D₆–CD₃CN in a ratio 9 : 1), the spectrum exhibits the sharp signals assignable to one Tp*, two SPh, and one Cp* groups together with the one free MeCN dissociated from the Ru site by replacement with CD₃CN. With respect to the Tp* resonances, signals due to the pyrazole groups appeared as two sets with an intensity ratio of 2 : 1, while those due to the SPh groups indicated that the two Ph groups are equivalent. These spectral features in C₆D₆–CD₃CN are diagnostic of the X-ray structure of 3a and the spectrum observed for the C₆D₆ solution may be explained by the presence of the equilibrium between two slowly interconverting species in C₆D₆, i.e.3a and the species generated by the dissociation of the coordinated MeCN from its Ru site.

Interestingly, it has turned out that when the reaction mixture of 2a with [(Cp*Ru)₄(µ₃-Cl)₄] was kept for a longer period in the absence of MeCN, a mixture of 3a and another bimetallic complex was produced, and this new complex has been characterized by X-ray analysis (vide infra) to be the singly bridged complex [Tp*RhCl(SPh)(µ–η¹-S-η⁶-Ph)RuCp*] (4a) depicted in Fig. 3 (Scheme 1). The ¹H NMR study of 3a in C₆D₆ showed that in the spectra initially exhibiting only the broad peaks of 3a, the sharp signals due to 4a appeared and their intensities increased gradually. This indicates unambiguously that 3a in solution is transformed slowly into 4a even at room temperature. On the other hand, when a benzene solution of 3a was heated at reflux, conversion of 3a into 4a was completed smoothly and 4a was isolated in 41% yield in a pure form.

Fig. 3 An ORTEP drawing for 4a at 30% probability level. Hydrogen atoms are omitted for clarity.

Reaction of the bis(selenolato) complex 2b with [(Cp*Ru)₄(µ₃-Cl)₄] also proceeded at room temperature to afford the doubly bridged complex [Tp*RhCl(µ-SePh)₂RuCp*(MeCN)] (3b). In contrast to 3a, however, the selenolato complex 3b in C₆D₆ shows the sharp ¹H NMR resonances diagnostic of its solid state structure determined by X-ray analysis and the spectra recorded after prolonged periods were identical when kept at room temperature. These findings indicate that in 3b the MeCN ligand is bonded to Ru tightly even in solution and the core structure is stable at room temperature. On the other hand, transformation into a singly bridged complex [Tp*RhCl(SePh)(µ–η¹-Se-η⁶-Ph)RuCp*] (4b) did also proceed for the selenolato complex 3b when more forcing conditions were employed, e.g. refluxing a benzene solution of 3b for 6 h. It is noteworthy that the tellurolato analogue [Tp*RhCl(µ-TePh)₂RuCp*(MeCN)] (3c), which was obtained by similar treatment of 2c with [(Cp*Ru)₄(µ₃-Cl)₄] and showed the ¹H NMR spectral feature analogous to 3b at room temperature, did not react even at refluxing temperature. Thus, 3c dissolved in benzene was recovered quantitatively after heating at reflux for 6 h (Scheme 1).

This core rearrangement, observed for 3a even at room temperature, and for 3b under more forcing conditions, but not for 3c, may proceed because of the presence of the steric hindrance in these doubly bridged complexes. Since the hindrance between the Tp*, Cp* and Ph groups decreases in the order 3a > 3b > 3c due to the elongation of the M–E bond distances, reactivities of 3 toward conversion into less sterically hindered 4 presumably decrease in this order. More labile features of the MeCN ligand observed for 3a to generate coordinatively unsaturated Ru center also arises from the steric crowding at the Ru site that is more severe in this thiolato complex than in 3b and 3c, and is presumably ascribable to the more facile core rearrangement observed for 3a.

Closely related rearrangement of the aryloxo ligand was reported previously for the coordinatively unsaturated Cp*Ru^II complexes [(Cp*Ru)₂(µ-OAr)₂] (Ar = Ph, C₆H₃PrⁱMe-2,5, C₆H₃Bu^t₂-3,4), which are gradually converted into mononuclear complexes [Cp*Ru(η⁵-OAr)] at room temperature.⁵ By contrast, the thiolato analogue [(Cp*Ru)₂(µ-SC₆H₃Me2-2,6)₂] is stable and does not undergo the core rearrangement of this type under similar conditions.⁶

X-Ray structures of 3a, 3b, and 4a

The X-ray structure of 3a depicted in Fig. 2 is compares well to that of the previously described [Tp*RhCl(µ-SPh)₂RhCp*(MeCN)]⁺.² Thus, the RhRuS₂ ring is almost planar, and the two metal centers connected by two mutually syn SPh ligands are separated by 3.6875(5) Å, which indicates the absence of any metal–metal bonding interactions. Two Ph groups of the µ-thiolato ligands are oriented toward the opposite direction to the Cp* ligand and one pyrazolyl Me group of the Tp* ligand occupies the sandwiched position between these two Ph rings.

As shown in Table 2, the Rh–S bond distances at 2.354(1) and 2.355(1) Å are significantly shorter than the Ru–S bond distances at 2.432(1) and 2.437(1) Å. The Tp*Rh–S bond lengths in 3a are comparable to those in [Tp*RhCl(µ-SPh)₂RhCp*(MeCN)]⁺ (2.357(2) and 2.371(2) Å) and other µ-thiolato and µ-hydrosulfido complexes cited in the previous paper.² With respect to the Ru–µ-S bond lengths, those in 3a are almost identical with those in [{Cp*Ru(CO)}₂(µ-SBu^t)₂] (2.422 Å (av.))⁷ or somewhat longer than those in the coordinatively unsaturated Cp*Ru^II complexes [(Cp*Ru)₂(µ-SC₆H₃Me₂-2,6)₂] (2.350 Å),⁶ and [{(η⁵-C₅Me₄Et)Ru}₂(µ-SEt)₂] (2.323 Å (av.)).⁸ For the related Ru^III complexes, the Ru-µ-S bond lengths at 2.314 Å (av.) in [(Cp*RuCl)₂(µ-SEt)₂]⁹ and 2.319 Å (av.) in [(Cp*RuCl)₂(µ-SPh)₂]¹⁰ have been reported.

Table 2 Selected bond distances (Å) and angles (°) in 3a and 3b

	3a (E = S)	3b (E = Se)
Rh–Cl	2.338(1)	2.353(1)
Rh–E(1)	2.354(1)	2.4769(6)
Rh–E(2)	2.355(1)	2.4775(4)
Rh–N(2)	2.128(4)	2.154(4)
Rh–N(4)	2.129(4)	2.143(3)
Rh–N(6)	2.098(3)	2.101(3)
Ru–E(1)	2.432(1)	2.5271(5)
Ru–E(2)	2.437(1)	2.5371(7)
Ru–N(7)	2.044(4)	2.038(4)
Ru–C(Cp*)	2.170(5)–2.191(5)	2.153(7)–2.183(5)
N(7)–C(38)	1.121(6)	1.125(7)
Rh⋯Ru	3.6875(5)	3.8585(5)
E(1)–Rh–E(2)	80.45(4)	80.19(2)
E(1)–Ru–E(2)	77.30(4)	78.12(2)
Rh–E(1)–Ru	100.80(4)	100.90(2)
Rh–E(2)–Ru	100.63(4)	100.61(2)

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The Se analogue 3b has essentially the same structure as that of 3a. Pertinent bond distances and angles observed for 3b are also listed in Table 2. The Rh–Se bonds at 2.4769(6) and 2.4775(4) Å and the Ru–Se bonds at 2.5271(5) and 2.5371(7) Å are longer than the corresponding Rh–S and Ru–S bonds in 3a by ca. 0.12 and 0.10 Å, which are consistent with the difference in the covalent radii of Se at 1.17 Å and S at 1.04 Å.⁴ Accordingly, the Rh⋯Ru separation of 3.8585(5) Å is longer than that in 3a by ca. 0.17 Å. Well defined µ-selenolato complexes of Rh and Ru are still limited; previously reported Rh–µ-Se bond lengths are 2.481 Å (av.) in [{CpRh(SePh)₂}(µ-SePh)₂] and 2.502 Å (av.) in [(Cp*Rh)₂(µ-SePh)₃]⁺,¹¹ while the Ru–µ-Se bond distances in the Ru^III complexes [(Cp*Ru)₂(µ-SeTol)₃]Cl,¹² [(Cp*RuCl)₂(µ-SeFc)₂] (Fc = ferrocenyl),¹³ [(Cp*RuCl)₂(µ-SeR)₂] (R = Me, Et, Prⁿ, Prⁱ, Ph),¹⁴ and [{CpRu(MeCN)}₂(µ-SePh)₂][PF₆]₂¹⁵ are 2.456 Å (av.), 2.4218 Å, 2.415(1)–2.439(1) Å, and 2.421 Å (av.), and those in the Ru^I complex [{Ru(CO)₂}₂(µ-SePh)₂(µ-Ph₂PCH₂PPh₂)]¹⁶ are 2.524 Å (av.), respectively.

On the other hand, Fig. 3 shows the molecular structure of 4a and Table 3 summarizes the important bond lengths and angles therein. Complex 4a has a dinuclear structure containing Tp*Rh and Cp*Ru units connected by one SPh ligand, which coordinates to the Rh center at the S atom in a terminal end-on mode and to the Ru atom by the Ph ring in an η⁶-fashion. The Rh center has an octahedral structure with a fac-Tp*, two PhS, and one Cl ligands. The Rh–S(1) bond associated with the µ-SPh ligand is somewhat elongated from the Rh–S(2) bond in the terminal SPh ligand. On the basis of the difference in the Rh–N bond distances (Rh–N(4): 2.125(4), Rh–N(2): 2.111(4), Rh–N(6): 2.088(4) Å), the strength of the trans influence of the thiolate and Cl ligands is assumed to decrease in the order: terminal S(2)–Ph > µ-S(1)–Ph > Cl. The Rh–S–C angles are essentially the same for both the terminal and bridging SPh ligands (112.4(2) and 113.7(2)°).

Table 3 Selected bond distances (Å) and angles (°) in 4a

Rh–Cl	2.359(1)	Rh–S(1)	2.358(1)
Rh–S(2)	2.331(2)	Rh–N(2)	2.111(4)
Rh–N(4)	2.125(4)	Rh–N(6)	2.088(4)
Ru–C(16)	2.276(5)	Ru–C(17)	2.228(6)
Ru–C(18)	2.200(6)	Ru–C(19)	2.193(6)
Ru–C(20)	2.170(6)	Ru–C(21)	2.197(6)
Ru–C(Cp*)	2.141(5)–2.165(6)
S(1)–Rh–S(2)	89.98(6)	Rh–S(1)–C(16)	113.7(2)
Rh–S(2)–C(22)	112.4(2)

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Around Ru, both of the Cp* and Ph groups coordinate to the Ru atom in a π-fashion and these two planes are mutually parallel with the dihedral angle of 177.4°. The Ru–C(Cp*) bond distances differ only slightly to each other, which are in the range 2.141(5)–2.165(6) Å. By contrast, the Ru–C(Ph) bond lengths vary significantly from 2.170(6) Å of the Ru–C(20) bond up to 2.276(5) Å of the Ru–C(16) bond, where the C(20) and C(16) atoms are occupying the meta and ipso positions of the SPh ligand, respectively. Elongated Ru–C(16) distance is interpreted in terms of the contribution of the resonance structure i for 4a as shown in eqn (2).

Formation of dioxygen complexes [Tp*RhCl(µ-EPh)₂RuCp*(η²-O₂)] (5)

By stirring the THF solutions of 3 under air at room temperature, dioxygen complexes 5 were obtained (eqn (3)). Three products 5a–5b were all isolated as single crystals in moderate yields and fully characterized by X-ray analyses. Since these three are isomorphous, an ORTEP drawing is depicted for 5a (Fig. 4) only. Important bond distances and angles in 5a–5c are listed in Table 4.

Table 4 Selected bond distances (Å) and angles (°) in 5

	5a (E = S)	5b (E = Se)	5c (E = Te)
Rh–Cl	2.3462(8)	2.349(2)	2.360(1)
Rh–E(1)	2.3588(8)	2.4590(7)	2.6185(4)
Rh–E(2)	2.3462(7)	2.4645(7)	2.6022(5)
Rh–N(2)	2.100(2)	2.115(5)	2.154(4)
Rh–N(4)	2.108(2)	2.118(4)	2.150(4)
Rh–N(6)	2.093(2)	2.091(5)	2.097(3)
Ru–E(1)	2.4294(7)	2.5461(7)	2.6900(4)
Ru–E(2)	2.4316(8)	2.5393(7)	2.6678(5)
Ru–O(1)	1.984(2)	2.008(4)	2.020(3)
Ru–O(2)	2.004(2)	1.994(4)	2.007(4)
Ru–C(Cp*)	2.191(3)–2.314(3)	2.189(6)–2.292(7)	2.205(5)–2.285(4)
Rh⋯Ru	3.7073(3)	3.8583(6)	4.0608(5)
O(1)–O(2)	1.397(3)	1.406(6)	1.383(6)
E(1)–Rh–E(2)	79.91(3)	80.62(2)	80.90(1)
E(1)–Ru–E(2)	76.86(2)	77.56(2)	78.42(1)
O(1)–Ru–O(2)	41.01(9)	41.1(2)	40.2(2)
Rh–E(1)–Ru	101.46(3)	100.85(2)	99.80(1)
Rh–E(2)–Ru	101.77(3)	100.89(2)	100.80(1)

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Fig. 4 An ORTEP drawing for 5a at 30% probability level. Hydrogen atoms are omitted for clarity. The structures and the atom numbering schemes are essentially the same for the Se and Te analogues 5b and 5c.

The structures of 5 are analogous to the corresponding 3 except for the presence of the η²-O₂ ligands in place of the η¹-MeCN ligands. Bonding parameters associated with the Rh(µ-EPh)₂Ru core for 5a and 5b are essentially the same as those of the X-ray analyzed counterparts 3a and 3b, respectively. In 5, the Rh–E and Ru–E bond distances are elongated from 2.352 and 2.431 Å (av.) in 5a (E = S) to 2.610 and 2.679 Å (av.) in 5c (E = Te) as the covalent radii of E increase, and accordingly the Rh⋯Ru separations become greater in this order from 3.7073(3) Å in 5a to 4.0608(5) Å in 5c. To our knowledge, there are no precedented examples of the Rh–µ-TeR bond lengths, while the Ru–Te bond distances for the µ-tellurolato ligands in the Ru^II complexes [(Cp*Ru)₂(µ-TeTol)₂(µ-TolTeTeTol)]¹² and [(Cp*Ru)₂(µ-TeFc)₂(µ-butadiene)]¹³ and in the Ru^III complexes [(Cp*RuCl)₂(µ-TeMe)₂]¹⁴ were reported to be 2.676 (av.), 2.659 (av.), and 2.580(1) Å, that for the µ-TePrⁱ ligand in the alkynylvinyl cluster [Ru₃Pt{µ₄-C(Ph)CCCH(Bu^t)}(µ₄-Te)(µ₂-TePrⁱ)(CO)₆(dppe)] being 2.655 Å (av.).¹⁷

The dioxygen molecule coordinates to the Ru center in an η² manner. The O–O bond lengths in the range 1.383(6)–1.406(6) Å for these three complexes are apparently not affected by the nature of the chalcogenolato ligands and are in the range typical to the peroxo ligands (1.35–1.5 Å).¹⁸ In the IR spectra of 5, however, no bands assignable to the O₂ ligands were observed, although the peroxo ligands generally show the characteristic ν(O–O) bands in the region 820–910 cm⁻¹. As the O₂ ligand is formulated as O₂²⁻, the formal oxidation state of the Ru center becomes +4 and the comparable O–O bond distances have been observed in the other Ru^IV peroxo complexes such as [RuH(η²-O₂)(C₆H₄-o-py)(PPrⁱ₃)₂] (py = pyridyl) (1.407(3) Å),¹⁹ [Cp*Ru(η²-O₂){Ni(S₂N₂)}]⁺ (S₂N₂ = SCH₂CH₂NMeCH₂CH₂NMeCH₂CH₂S) (1.371(8) Å),²⁰ and [Cp*Ru(η²-O₂)(P₂)]⁺ (P₂ = dppe: 1.398(5) Å;²¹P₂ = dppm: 1.37(1) Ų²). In contrast, the O–O distance at 1.461(5) Å in the Ru^II peroxo complex [Ru(η²-O₂)(Ph₂PNMeNMePPh₂)₂]²³ is much longer and comparable to that in the H₂O₂ (1.461(3) Å).²⁴ Reactivities of the peroxo ligands in 5 are now under investigation.

Experimental

General considerations

All manipulations were carried out under N₂ using standard Schlenk techniques. Solvents were dried by common procedures and distilled under N₂ before use. Complexes 1²⁵ and [(Cp*Ru)₄(µ₃-Cl)₄]²⁶ were prepared according to literature methods, while other reagents were commercially obtained and used as received.

¹H NMR spectra were recorded on a JEOL alpha-400 spectrometer (400 MHz), where the chemical shifts were referred to those of the impurities in deuterated solvents (δ 7.26 for CDCl₃ and 7.15 for C₆D₆). IR spectra were recorded on a JASCO FT/IR-420 spectrometer and elemental analyses were performed with a Perkin-Elmer 2400 series II CHN analyzer.

[Tp*Rh(SePh)₂(MeCN)] (2b). To a solution of 1 (739 mg, 1.34 mmol) in benzene (40 mL) was added PhSeSePh (425 mg, 1.36 mmol) and the mixture was stirred at room temperature for 4 h. The resultant mixture was dried in vacuo and the residue was extracted with THF. Addition of hexane to the concentrated extract afforded 2b as red crystals (713 mg, 71% yield). Found: C, 45.89; H, 4.45; N, 12.98. C₂₉H₃₅N₇BSe₂Rh requires C, 46.24; H, 4.68; N, 13.02%. δ_H (C₆D₆): 0.52 (s, 3H, MeCN), 2.18, 3.40 (s, 3H each, Me in Tp*), 2.20, 2.60 (s, 6H each, Me in Tp*), 5.44 (s, 1H, CH in Tp*), 5.60 (s, 2H, CH in Tp*), 6.83 (t, 4H, m-H in Ph), 6.87 (t, 2H, p-H in Ph), 7.35 (d, 4H, o-H in Ph). IR (KBr): 2527 (B–H), 2327 (C≡N) cm⁻¹.

[Tp*Rh(TePh)₂(MeCN)] (2c). To a toluene solution (40 mL) of 1 (937 mg, 1.70 mmol) was added PhTeTePh (712 mg, 1.73 mmol) at −20 °C and the mixture was continuously stirred at this temperature for 1 day. Addition of hexane to the concentrated product solution afforded 2c as green crystals (963 mg, 66% yield). Found: C, 40.76; H, 4.15; N, 11.87. C₂₉H₃₅N₇BTe₂Rh requires C, 40.95; H, 4.15; N, 11.53%. δ_H (C₆D₆): 0.47 (s, 3H, MeCN), 2.16, 3.46 (s, 3H each, Me in Tp*), 2.19, 2.59 (s, 6H each, Me in Tp*), 5.45 (s, 1H, CH in Tp*), 5.59 (s, 2H, CH in Tp*), 6.72 (t, 4H, m-H in Ph), 6.88 (t, 2H, p-H in Ph), 7.54 (d, 4H, o-H in Ph). IR (KBr): 2525 (B–H), 2332 (C≡N) cm⁻¹.

[Tp*RhCl(µ-SPh)₂RuCp*(MeCN)] (3a). To a mixture of 2a (51 mg, 0.077 mmol) and [(Cp*Ru)₄(µ₃-Cl)₄] (21 mg, 0.019 mmol) both in a solid state was added THF (3 mL) and MeCN (0.1 mL), and the mixture was stirred at room temperature for 5 min. Addition of hexane (15 mL) to the resultant red solution gave red–purple crystals of 3a, which were filtered off, washed with hexane, and then dried in vacuo (53 mg, 74% yield). Found: C, 50.23; H, 5.41; N, 10.29. C₃₉H₅₀N₇BS₂ClRhRu requires C, 50.30; H, 5.41; N, 10.53%. δ_H (C₆D₆–CD₃CN (9:1)): 0.99 (s, 3H, MeCN dissociated from Ru), 1.30 (s, 3H, Me in Tp*), 1.89 (s, 15H, Cp*), 2.23 (br, 3H + 6H, overlapping two singlets, Me in Tp*), 3.11 (s, 6H, Me in Tp*), 5.35 (s, 1H, CH in Tp*), 5.63 (s, 2H, CH in Tp*), 6.6–6.7 (m, 6H, m- and p-H in Ph), 6.9–7.1 (m, 4H, o-H in Ph). IR (KBr): 2530 (B–H), 2258 (C≡N) cm⁻¹. Single crystals of 3a·THF for the X-ray diffraction were grown from THF–MeCN–hexane at −20 °C.

[Tp*RhCl(µ-SePh)₂RuCp*(MeCN)] (3b). A mixture of 2b (148 mg, 0.197 mmol) and [(Cp*Ru)₄(µ₃-Cl)₄] (54 mg, 0.050 mmol) in THF (10 mL) was stirred for 4 h at room temperature, and the resultant solution was concentrated. Addition of hexane gave 3b·2.625THF as dark red crystals (50 mg, 26% yield). Found: C, 49.33; H, 5.78; N, 8.10. C_49.5H₇₁N₇O_2.625BSe₂ClRhRu requires C, 48.96; H, 5.89; N, 8.07%. δ_H (C₆D₆): 1.20, 1.31 (s, 3H each, MeCN and Me in Tp*), 1.40 (m, 12H, THF), 1.96 (s, 15H, Cp*), 2.18, 3.34 (s, 6H each, Me in Tp*), 2.29 (s, 3H, Me in Tp*), 3.57 (m, 12H, THF), 5.44 (s, 1H, CH in Tp*), 5.60 (s, 2H, CH in Tp*), 6.63 (t, 4H, m-H in Ph), 6.79 (t, 2H, p-H in Ph), 7.17 (d, 4H, o-H in Ph). IR (KBr): 2527 (B–H), 2278 (C≡N) cm⁻¹.

[Tp*RhCl(µ-TePh)₂RuCp*(MeCN)] (3c). This complex was prepared from 2c (684 mg, 0.803 mmol) and [(Cp*Ru)₄(µ₃-Cl)₄] (217 mg, 0.200 mmol) by the same method as that for synthesizing 3b. The yield of 3c·THF as dark red crystals was 577 mg (60%). Found: C, 42.89; H, 4.83; N, 8.06. C₄₃H₅₈N₇OBTe₂ClRhRu requires C, 43.24; H, 4.89; N, 8.21%. δ_H (C₆D₆): 1.15, 1.18 (s, 3H each, MeCN and Me in Tp*), 1.40 (m, 4H, THF), 1.97 (s, 15H, Cp*), 2.23, 3.33 (s, 6H each, Me in Tp*), 2.34 (s, 3H, Me in Tp*), 3.57 (m, 4H, THF), 5.40 (s, 1H, CH in Tp*), 5.63 (s, 2H, CH in Tp*), 6.55 (t, 4H, m-H in Ph), 6.83 (t, 2H, p-H in Ph), 7.20 (d, 4H, o-H in Ph). IR (KBr): 2522 (B–H), 2250 (C≡N) cm⁻¹.

[Tp*RhCl(SPh)(µ-η¹-S-η⁶-Ph)RuCp*] (4a). A mixture of 2a (82 mg, 0.12 mmol) and [(Cp*Ru)₄(µ₃-Cl)₄] (34 mg, 0.031 mmol) in THF (5 mL) was stirred at room temperature for 19 h. A small amount of red–purple solid precipitated, which was characterized to be 3a. Filtration of the mixture followed by addition of hexane (15 mL) to the filtrate afforded 3a as microcrystals (32 mg, 28% yield) and 4a·THF as orange prisms (40 mg, 34% yield) after one week. Found: C, 51.21; H, 5.89; N, 8.66. C₄₁H₅₅ON₆BS₂ClRhRu requires C, 51.17; H, 5.76; N, 8.73. δ_H (C₆D₆): 1.47 (s, 15H, Cp*), 2.24, 2.26, 2.27, 3.08, 3.23, 3.25 (s, 3H each, Me in Tp*), 4.26 (t, J = 6 Hz, 1H, p-H of η⁶-Ph), 4.37, 4.46 (t, J = 6 Hz, 1H each, m-H of η⁶-Ph), 5.50, 5.58, 5.74 (s, 1H each, CH in Tp*), 6.22 (d, J = 6 Hz, 1H, one o-H of η⁶-Ph), 6.6–6.9 (m, 6H, one o-H of η⁶-Ph and 5H of η¹-SPh), 1.40, 3.57 (m, 4H each, THF). IR (KBr): 2524 (B–H) cm⁻¹.

A benzene solution (15 mL) of 3a·THF (271 mg, 0.270 mmol) was refluxed for 6 h and the resultant mixture was filtered off and the orange solid remaining was extracted with CH₂Cl₂. Addition of hexane to the concentrated extract afforded 4a as orange–red crystals (133 mg, 55% yield).

[Tp*RhCl(SePh)(µ–η¹-Se-η⁶-Ph)RuCp*] (4b). A solution of 3b·3THF (63 mg, 0.051 mmol) in benzene (5 mL) was refluxed for 6 h and the resultant mixture was filtered off. A red solid remained, which was extracted with CH₂Cl₂. Addition of hexane to the concentrated extract afforded 4b as red crystals (36 mg, 72% yield). Found: C, 44.97; H, 4.90; N, 8.46. C₃₇H₄₇N₆BSe₂ClRhRu requires C, 45.16; H, 4.81; N, 8.54%. δ_H (CDCl₃): 1.98 (s, 15H, Cp*), 2.35, 2.36, 2.41, 2.60, 2.77, 2.83 (s, 3H each, Me in Tp*), 5.29–5.37 (m, 3H, m- and p-H of η⁶-Ph), 5.49, 5.58, 5.75 (s, 1H each, CH in Tp*), 6.19 (d, J = 5 Hz, 1H, one o-H of η¹-SePh), 6.32 (d, J = 8 Hz, 2H, o-H of η¹-SePh), 6.50 (t, J = 8 Hz, 2H, m-H of η¹-SePh), 6.63–6.73 (m, 2H, 1H of η⁶-Ph and o-H of η¹-SePh). IR (KBr): 2526 (B–H) cm⁻¹.

[Tp*RhCl(µ-SPh)₂RuCp*(η²-O₂)] (5a). A THF solution (20 mL) of 3a·THF (264 mg, 0.263 mmol) was stirred at room temperature for 12 h under air. Addition of hexane to the concentrated product solution gave red–brown crystals of 5a·THF (173 mg, 66% yield). Found: C, 49.41; H, 5.43; N, 8.06. C₄₁H₅₅N₆O₃BS₂ClRhRu requires C, 49.53; H, 5.58; N, 8.45%. δ_H (C₆D₆): 1.40 (m, 4H, THF), 1.57 (s, 15H, Cp*), 1.64, 2.14 (s, 3H each, Me in Tp*), 2.11, 3.04 (s, 6H each, Me in Tp*), 3.57 (m, 4H, THF), 5.22 (s, 1H, CH in Tp*), 5.53 (s, 2H, CH in Tp*), 6.82 (t, 4H, m-Ph), 6.84 (t, 2H, p-Ph), 7.19 (d, 4H, o-Ph). IR (KBr): 2533 (B–H) cm⁻¹.

[Tp*RhCl(µ-SePh)₂RuCp*(η²-O₂)] (5b). This complex was obtained as red–brown crystals of 5b·THF (34 mg, 72% yield) from 3b·3THF (48 mg, 0.046 mmol) by the same method as that for preparing 5a. Found: C, 44.91; H, 4.84; N, 7.88. C₄₁H₅₅N₆O₃BSe₂ClRhRu requires C, 45.26; H, 5.09; N, 7.72%. δ_H (C₆D₆): 1.41 (m, 4H, THF), 1.53 (s, 15H, Cp*), 1.58, 2.18 (s, 3H each, Me in Tp*), 2.17, 3.09 (s, 6H each, Me in Tp*), 3.56 (m, 4H, THF), 5.20 (s, 1H, CH in Tp*), 5.53 (s, 2H, CH in Tp*), 6.78 (t, 4H, m-Ph), 6.84 (t, 2H, p-Ph), 7.31 (d, 4H, o-Ph). IR (KBr): 2532 (B–H) cm⁻¹.

[Tp*RhCl(µ-TePh)₂RuCp*(η²-O₂)] (5c). This complex was also obtained as red–brown crystals of 5c·THF (39 mg, 52% yield) from 3c·3THF (76 mg, 0.068 mmol) by the same method as that for preparing 5a. Found: C, 41.51; H, 4.56; N, 6.90. C₄₁H₅₅N₆O₃BTe₂ClRhRu requires C, 41.54; H, 4.68; N, 7.09%. δ_H (C₆D₆): 1.40 (m, 4H, THF), 1.65 (s, 15H, Cp*), 1.34 (s, 3H, Me in Tp*), 2.17 (s, overlapping two singlets of 3H and 6H, Me in Tp*), 3.12 (s, 6H, Me in Tp*), 3.57 (m, 4H, THF), 5.12 (s, 1H, CH in Tp*), 5.59 (s, 2H, CH in Tp*), 6.72 (t, 4H, m-Ph), 6.84 (t, 2H, p-Ph), 7.41 (d, 4H, o-Ph). IR (KBr): 2550 (B–H) cm⁻¹.

Crystallography

Single crystals of 2b, 3a·THF, 3b·2.625THF, 4a·THF, 5a·THF, 5b·THF, and 5c·THF were sealed in glass capillaries under argon and mounted on a Rigaku Mercury-CCD diffractometer equipped with a graphite-monochromatized Mo-Kα source. All diffraction studies were performed at 23 °C, whose details are listed in Table 5.

Table 5 X-Ray crystallographic data for 2c, 3a, 3b, 4a, 5a, 5b, and 5c

	2c	3a·THF	3b·2.625THF	4a·THF	5a·THF	5b·THF	5c·THF
a R1 = Σ‖ Fo| − |Fc‖/Σ|Fo|. Based on the data with I > 2σ(I). b wR2 = [Σw(Fo^2 − Fc^2)^2/Σ w(Fo^2)^2]^1/2. Based on all data. c GOF = [Σ w(|Fo| − |Fc|)^2/{(no. observed) − (no. variables)}]^1/2.
Formula	C29H35N7BTe2Rh	C43H58N7OBS2ClRhRu	C49.5H71N7O2.625BSe2ClRhRu	C41H55N6OBS2ClRhRu	C41H55N6O3BS2ClRhRu	C41H55N6O3BSe2ClRhRu	C41H55N6O3BTe2ClRhRu
Formula weight	850.56	1003.34	1214.39	962.28	994.28	1088.08	1185.36
Space group	P21/a (no. 14)	P21/c (no. 14)	P-1 (no. 2)	P21/c (no. 14)	P21/c (no. 14)	P21/c (no. 14)	P21/c (no. 14)
a/Å	8.189(3)	11.055(2)	12.159(2)	12.797(5)	11.224(2)	11.233(2)	11.439(2)
b/Å	23.512(9)	19.403(3)	13.757(2)	17.828(6)	19.355(4)	19.361(3)	12.020(2)
c/Å	17.625(7)	22.302(3)	18.045(2)	20.634(8)	20.168(4)	20.392(3)	32.913(7)
α/°	90	90	72.811(5)	90	90	90	90
β/°	97.054(2)	90.538(7)	78.756(6)	106.032(2)	92.093(1)	92.5895(7)	96.2910(8)
γ/°	90	90	78.868(6)	90	90	90	90
U/Å^3	3368(2)	4783(1)	2798.4(6)	4524(3)	4379(2)	4431(1)	4498(2)
Z	4	4	2	4	4	4	4
µ/cm^−1	22.33	8.42	19.56	8.86	9.22	24.60	20.76
Total reflections	7981	11380	13051	10747	10309	10542	10059
Data with I > 2σ(I)	3551	6275	8494	4580	7867	5824	7261
Variables	399	575	656	528	563	563	563
R1^a	0.050	0.042	0.043	0.048	0.037	0.045	0.037
wR2^b	0.163	0.134	0.134	0.156	0.112	0.139	0.114
GOF^c	1.02	1.00	1.06	1.02	1.02	1.03	1.00

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Structure solution and refinements were carried out by using the CrystalStructure program package.²⁷ The positions of the non-hydrogen atoms were determined by Patterson methods (PATTY)²⁸ and subsequent Fourier synthesis (DIRDIF 99).²⁹ These were refined with anisotropic thermal parameters by full-matrix least-squares techniques except for compounds 3b and 4a in which 5 and 1 atoms, respectively, were refined isotropically. Hydrogen atoms bound to the B atoms were found in the Fourier maps and refined isotropically, while all other hydrogens were placed at the calculated positions and included at the final stages of the refinements with fixed parameters. For 4a·THF, solvating THF molecule is occupying the disordered positions, which has been modeled as two differently oriented five-membered rings overlapping each other with the occupancies 1 : 1.

For 2b, only the preliminary results were obtained. Crystallographic data are as follows. 2b: C₂₉H₃₅N₇BSe₂Rh, M = 753.28, space group P2₁/n (no. 14), a = 19.762(8), b = 8.354(3), c = 19.128(8) Å, β = 101.213(6)°, U = 3098(2) ų, Z = 4, µ = 29.32 cm⁻¹, 5848 data (I > 3σ(I)), 396 variables, R1 = 0.083, wR2 = 0.170. Attempts to lower the R values to the satisfactory levels were unsuccessful.

CCDC reference numbers 265326–265332.

See http://dx.doi.org/10.1039/b503153m for crystallographic data in CIF or other electronic format.

Acknowledgements

This work was supported by Grant-in-Aid for Scientific Research on Priority Areas (No. 14078206, “Reaction Control of Dynamic Complexes”) from the Ministry of Education, Culture, Sports, Science and Technology, Japan and by CREST of JST (Japan Science and Technology Agency).

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