Half-Sandwich B-Oxy Boratabenzene Ruthenium Complexes

Article pubs.acs.org/Organometallics

Half-Sandwich B‑Oxy Boratabenzene Ruthenium Complexes: Synthesis, Characterization, and Reactivity of (η6‑C5H5BOR)RuCl(PPh3)2 (R = Et, Me) Ting Li, Chen Fu, Zi Liu, Shuiliang Guo, Zicheng Liu, and Ting-Bin Wen* Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P.R. China S Supporting Information *

ABSTRACT: The first examples of half-sandwich boratabenzene ruthenium complexes have been prepared and wellcharacterized. Treatment of RuCl2(PPh3)3 with the anionic boratabenzene ligands C5H5BORNa (R = Et, Me) produced the B-alkoxy complexes (η6-C5H5BOR)RuCl((PPh3)2 (R = Et, 1a; Me, 1b), while the reaction of RuCl2(PPh3)3 with the neutral borabenzene−PPh3 adduct C5H5BPPh3 led to the formation of the dinuclear complex (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2), with an oxo-bis(boratabenzene) bridging ligand connected by the B−O−B linkage. The B-hydroxy complex (η6-C5H5BOH)RuCl(PPh3)2 (3) was obtained from the nucleophilic substitution of complexes 1a, 1b, or 2 with water at the boron atoms, and the complexes 1a, 1b, 2, and 3 could interconvert through the nucleophilic substitution reactions. While the reaction of 1a with phenylacetylene did not successfully afford the vinylidene complex as expected, reactions of 1a with terminal ω-alkynols HCC(CH2)nCH(R)OH (R = H, n = 1, 2; R = Me, n = 1) proceeded smoothly to provide the neutral oxacyclocarbene complexes (η6-C5H5BOEt)RuCl( CCH2CH2CH2O)(PPh3) (4), (η6-C5H5BOEt)RuCl(CCH2CH2CH2CH2O)(PPh3) (5), and (η6-C5H5BOEt)RuCl(CCH2CH2CH(Me)O)(PPh3) (6) via intramolecular nucleophilic attack of the hydroxyl group to the corresponding vinylidene intermediates.

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INTRODUCTION

modulated by the choice of the exocyclic boron substituent of the boratabenzene ligands, which renders the reactivity control much easier for boratabenzene complexes as compared to the Cp-based complexes.2c,d,4 In the past three decades, significant progress has been made in the boratabenzene chemistry, and numerous transition-metal complexes bearing boratabenzene ligands have been reported, some of which display interesting structural features or unusual reactivities.5 On the other hand, half-sandwich cyclopentadienyl ruthenium complexes play a key role in the development of organometallic chemistry.6,7 They exhibit a particularly rich and interesting chemistry, which includes diversified stoichiometric reactivities6 and catalytic transformations involving C−C and C−heteroatom coupling reactions,7,8 as well as serving as useful building blocks for supramolecular chemistry.9 Recent reports have also described their potential application in medicinal chemistry due to the unusual biological activities.10 In view of the versatile roles of half-sandwich cyclopentadienyl ruthenium complexes and the aforementioned achievements in boratabenzene transition-metal chemistry, there has been great potential to develop the chemistry of half-sandwich boratabenzene ruthenium complexes. However, half-sandwich borata-

Cyclopentadienyl (Cp) and its derivatives are among the most important ligands in organometallic chemistry, and transitionmetal complexes bearing Cp-type ligands have been applied in a wide range of fields.1 These investigations have spurred interest in the development of heterocyclic boron-containing Cp analogues as alternatives to the ubiquitous Cp ligands, especially in the pursuit of new, efficient catalysts.2 In this regard, boratabenzenes, a type of 6π-electron aromatic anions, have been introduced into organometallic chemistry to serve as isoelectronic six-membered-ring analogues of Cp (Chart 1).3,4 In general, boratabenzenes are weaker donors than Cp ligands and thus can generate more-electrophilic metal centers. Besides, the electron density of the metal center can be conveniently Chart 1. Cyclopentadienyl, Neutral Borabenzene, and Anionic Boratabenzene Ligands

Received: April 16, 2015

© XXXX American Chemical Society

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DOI: 10.1021/acs.organomet.5b00319 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

complexes exclusively instead of the thermodynamically favored bis-boratabenzene ruthenocene complex. The definite structures of complexes (η6-C5H5BOR)RuCl(PPh3)2 (R = Et, 1a; Me, 1b) have been confirmed by X-ray diffraction as shown in Figures 1 and 2, from which we can see

benzene ruthenium complexes have not been reported before now. In fact, to the best of our knowledge, the boratabenzene derivatives of ruthenium are still rather limited to a few examples of sandwich and triple-decker sandwich11 complexes, and their chemistry remains mostly unexplored. As part of our investigation on the chemistry of halfsandwich ruthenium complexes bearing boron-containing heterocyclic ligands, we have recently reported the synthesis of the first half-sandwich 1,2-azaborolyl (Ab) ruthenium complex, (Ab-CCPh)RuCl(PPh3)2 (Ab-CCPh = l-tertbutyl-2-phenylethynyl-1,2-azaborolyl), which can act as an efficient catalyst precursor for [2+2] cycloaddition of norbornene derivatives with dimethyl acetylenedicarboxylate and also for the radical additions of olefins with polyhalogenated compounds, competing favorably with respect to the Cp congeners CpRuCl(PPh3)2 and Cp*RuCl(PPh3)2.12 We now extend our studies to develop the chemistry of halfsandwich boratabenzene ruthenium complexes. In this work, we report the synthesis of a series of such complexes, including the B-alkoxy and B-hydroxy complexes (η6-C5H5BOR)RuCl(PPh3)2 (R = Et, 1a; Me, 1b; H, 3) and the oxobis(boratabenzene) bridged dinuclear complex (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2), which represent the first examples of half-sandwich boratabenzene ruthenium complexes. The interconversion between these complexes through nucleophilic substitution reactions at the boron atom and the reactivity of (η6-C5H5BOEt)RuCl(PPh3)2 (1a) toward phenylacetylene and terminal ω-alkynols are also investigated.

Figure 1. Molecular structure of the complex 1a drawn with 30% probability ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−B1 2.518(3), Ru1−C1 2.307(3), Ru1−C2 2.235(3), Ru1−C3 2.197(3), Ru1−C4 2.226(3), Ru1−C5 2.317(3), B1−O1 1.390(4), O1−C6 1.427(4), C6−C7 1.498(4), Ru1−Cl1 2.4271(7), Ru1−P1 2.3300(8), Ru1−P2 2.3471(9); P1−Ru1−P2 97.08(3), P1−Ru1−Cl1 89.86(3), P2− Ru1−Cl1 93.64(3), B1−O1−C6 119.2(3).

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RESULTS AND DISCUSSION Synthesis and Characterization of Half-Sandwich BAlkoxy Boratabenzene Ruthenium Complexes (η6-C5H5BOR)RuCl(PPh3)2 (R = Et, 1a; Me, 1b). The chemistry of cyclopentadienyl half-sandwich ruthenium complexes has been based largely on the precursor CpRuCl(PPh3)2, which is very useful for organometallic synthesis and catalysis.6a,b,7b−d,13 In this regard, it is desirable to prepare analogous boratabenzene complexes of this type. In light of the easy preparation of CpRuCl(PPh3)2 and Cp′RuCl(PPh3)2 (Cp′ = substituted Cp) from the reaction of RuCl2(PPh3)3 with the metal salts of Cp or Cp′ anion,14 and the advantages of the anionic alkoxyboratabenzene ligands shown in the preparation of boratabenzene complexes,15 we have investigated the reaction of RuCl2(PPh3)3 with C5H5BORNa (R = Et, Me). The boratabenzene ligands C5H5BORNa (R = Et, Me) can be prepared following the procedure reported by Fu.16 To our delight, treatment of RuCl2(PPh3)3 with C5H5BORNa (R = Et, Me) in a ratio of 1:1.1 in toluene at reflux temperature produced the expected half-sandwich complexes (η6-C5H5BOR)RuCl(PPh3)2 (R = Et, 1a; Me, 1b) as yellow solids in 70−80% yields (Scheme 1). It should be mentioned that the reaction of RuCl2(PPh3)2 with 2.0 equiv of the anionic ligands also gave the half-sandwich

Figure 2. Molecular structure of the complex 1b drawn with 30% probability ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−B1 2.539(5), Ru1−C1 2.305(4), Ru1−C2 2.193(4), Ru1−C3 2.202(4), Ru1−C4 2.229(4), Ru1−C5 2.301(4), B1−O1 1.362(5), O1−C6 1.442(5), Ru1−Cl1 2.4307(9), Ru1−P1 2.3443(10), Ru1−P2 2.3490(11); P1−Ru1−P2 96.61(4), P1−Ru1−Cl1 94.71(3), P2−Ru1−Cl1 90.55(4), B1−O1− C6 119.1(3).

Scheme 1. Preparation of Half-Sandwich Boratabenzene Ruthenium Complexes 1a and 1b

that 1a and 1b adopt similar piano stool structures, with two PPh3 ligands and a Cl ligand as the three legs. Taking 1a for example, the ruthenium atom tends to coordinate to the boratabenzene ligand, slipping away from the boron atom (Ru−B, 2.518(3) Å) and becoming more tightly bound to the ring carbon atoms (Ru−C, 2.197(3)−2.317(3) Å). The bond distances of Ru−Cl (2.4271(7) Å) and Ru−P (2.3300(8) and 2.3471(9) Å) are in keeping with those reported in CpRuClB


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Organometallics

along with other newly formed unidentified species. When the solution was heated at 85 °C for 8 h, RuCl2(PPh3)3 was completely consumed, and the reaction turned messy, however. The complicated 31P{1H} NMR signals of the solution indicated formation of a mixture of unknown species but without a dominant one. A small amount of cis-RuCl2(PMe3)4 was crystallized from the solution after prolonged standing at RT.19 We thus suspect that the PMe3 liberated from C5H5BPMe3 could in turn react with RuCl2(PPh3)3 to give a mixture of ruthenium species such as RuCl2(PPh3)m(PMe3)n, which then resulted in the complicated reaction. Consequently, we turned our attention to the reaction of borabenzene C5H5BPPh3 with RuCl2(PPh3)3 to avoid the ligand redistribution between PMe3 and PPh3 in the reaction solution, so that the intended cationic half-sandwich borabenzene ruthenium complex 2′ might be obtained (Scheme 2).

(PPh3)2 (Ru−Cl, 2.453(2) Å; Ru−P, 2.337(1) and 2.335(1) Å)17 and Cp*RuCl(PPh3)2 (Ru−Cl, 2.4583(6) Å; Ru−P, 2.3379(6) and 2.3464(5) Å).18 The P−Ru−Cl angles (P1− Ru1−Cl1 89.86(3)°, P2−Ru1−Cl1 93.64(3)°) are similar to those in CpRuCl(PPh3)2 (89.05(3)° and 90.41(4)°) and Cp*RuCl(PPh3)2 (87.9(1)° and 93.4(1)°), and the P−Ru−P angle (P1−Ru1−P2 97.08(3)°) is significantly smaller than that of CpRuCl(PPh3)2 (103.99(4)°), but similar to that of Cp*RuCl(PPh3)2 (96.8(1)°). The relative steric bulkiness for the boratabenzene, Cp and Cp* ligands thereby might be reflected by the sum of bond angles between the three facial binding Cl and PPh3 ligands in 1a (280.58°), CpRuCl(PPh3)2 (283.45°), and Cp*RuCl(PPh3)2 (278.1°) to a certain extent, with the boratabenzene ligand being intermediate between Cp and Cp*. The alkoxy group bound to the boron atom is notably oriented away from the PPh3 ligands to minimize the steric interaction. The B1−O1−C6 angle of 119.2(3)° and the short B1−O1 distance of 1.390(4) Å are close to those reported for the alkoxyboratabenzene complexes [η6-C5H5BOEt]2ZrCl215a,b and [η6-C5H5BOMe]2Co,15c which suggest the sp2 hybridization of the oxygen atom and considerable π overlap between the B and O atoms in 1a.15 Consistently, the alkoxy group in 1a is nearly coplanar with the boratabenzene ring, with a small dihedral angle of 5.5(5)° between them. The solid-state structure of 1a is fully supported by NMR spectroscopy. The 31P{1H} NMR spectrum showed one singlet at 30.7 ppm, indicating that the two PPh3 ligands attach to the ruthenium center were symmetrical in chemical environment. Meanwhile, the 1H NMR (in C6D6) spectrum showed three resonances for the five proton signals on the boratabenzene ring at 5.26 (dd, 3J(HH) = 8.1 Hz, 5.0 Hz, 2H, BCHCH), 3.87 (t, 3J(HH) = 5.0 Hz, 1H, BCHCHCH), and 2.98 (d, 3J(HH) = 8.1 Hz, 2H, BCH) ppm in a ratio of 2:1:2. The three kind of carbons of the boratabenzen ring were observed at 108.4 (s, BCHCH), 73.2 (br, BCH), and 72.7 (br, BCHCHCH) ppm in the 13C{1H} NMR spectrum. Complex 1b has a structure similar to that of 1a, which deserves no further comments. Preparation of Oxo-bis(boratabenzene) Bridged Dinuclear Complex (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2) and B-Hydroxy Boratabenzene Complex (η6-C5H5BOH)RuCl((PPh3)2 (3) and Interconversion of 1a, 1b, 2, and 3. The family of boratabenzenes generally consists of neutral borabenzene−Lewis base adducts and anionic boratabenzene (Chart 1).4 Although examples of metal complexes with neutral borabenzene ligand are much less common than boratabenzene−metal complexes, a few examples of such complexes have been reported, specifically those coordinated by Cr0(CO)3,16b,19 involving the borabenzene−PMe3 complex (η6-C5H5BPMe3)Cr(CO)3.16b Thus, we have also investigated the reaction of RuCl2(PPh3)3 with the borabenzene ligand C5H5BPMe3, with the intention to obtain the corresponding half-sandwich borabenzene complex. When the reaction of RuCl2(PPh3)3 and C5H5BPMe3 (in a ratio of 1:1) in a C6D6 solution at RT was monitored by the in situ 31P{1H} NMR, it was found that C5H5BPMe3 was completely converted to the borabenzene−PPh3 adduct C5H5BPPh3 within 1 h due to the rapid replacement of the PMe3 ligand bound to the boron atom by the PPh3 dissociated from RuCl2(PPh3)3, as reflected by the disappearance of the 31P{1H} NMR signal of C5H5BPMe3 and concomitant appearance of a broad signal at ca. 6 ppm due to C5H5BPPh3 (vide inf ra). However, no signal of the free PMe3 could be detected, and the starting material RuCl2(PPh3)3 was evidenced as the predominant species in the reaction solution

Scheme 2. Preparation of Oxo-bis(boratabenzene) Bridged Dinuclear Ruthenium Complex 2

The borabenzene C5H5BbPPh3 was readily prepared by a similar procedure reported by Fu for the preparation of C5H5BPMe3,16 using PPh3 as the nucleophile instead of PMe3 to react with the borotacycle 1-chloro-2-(trimethylsilyl)boracyclohexa-2,5-diene. A toluene solution of RuCl2(PPh3)3 and C5H5BPPh3 in a ratio of 1:1 was then allowed to stir at reflux temperature for about 4 h, and a yellow solid was precipitated out, which was isolated (in approximately 20% yield) and identified to be the unexpected dinuclear complex (μ2-η6,η6C5H5BOBC5H5)[RuCl(PPh3)2]2 (2), with an oxo-bis(boratabenzene) bridging ligand connected by the B−O−B linkage. The oxygen is likely derived from the trace amount of water present in the solvent. Further studies revealed that, when the reaction was carried out in a degassed wet THF solution, the yield of 2 could be increased to 84%, while the yield of 2 dropped to 5% if the reaction was performed using freshly distilled THF as the solvent. The structure of 2 has been verified by X-ray diffraction. As shown in Figure 3, the most interesting aspect of the structure is the presence of a μ2-η6,η6-oxo-bis(boratabenzene) bridging ligand. Consequently, the molecule consists of two almost identical half-sandwich units with structural features similar to those of 1a and 1b, and a B−O−B bridge linking the two. The bond lengths of Ru−B (Ru1−B1, 2.517(5) Å; Ru2−B2, 2.546(5) Å) and Ru−C (2.203(4)−2.331(4) Å) are close to those in 1a and 1b, again indicating a slippage of Ru away from the boron atom and toward the ring carbon atoms. The B−O bond lengths (B1−O1, 1.378(6) Å; B2−O1 1.388(6) Å) and the B1−O1−B2 bond angle (130.9(4)°) are similar to those observed for the closely related complex [μ2-η6,η6-(3,5Me2C5H3B)O(3,5-Me2C5H3B)](CoCb*)2 (Cb* = tetramethylcyclobutadiene) reported by Herberich (B−O, 1.367(10) and 1.404(11) Å); B−O−B, 131.1(7)°),21 which is the only example of previously reported oxo-bis(boratabenzene) bridged dinuclear complex. The two boratabenzene rings in 2 are essentially coplanar with the oxygen atom but twist with respect to each other, with a dihedral angle of 13.33(12)° between C


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Organometallics

cyclohexa-2,4-dienes has been reported by Bazan.15b Coordination of the diene in 2A to RuCl2(PPh3)3 is expected to give the η4-diene intermediate 2B, which is then followed by elimination of a molecule of HCl with the help of the liberated PPh3 to produce the hydroxyboratabenzene complex 3. This step is similar to the preparation of cyclopentendienyl complexes Cp′RuCl(PPh3)2 (Cp′ = substituted Cp) from the reaction of RuCl2(PPh3)3 with Cp′H.22 The final product 2 could thus be formed from 3 via elimination of a molecule of H2O. Consistent with this proposition, compound 2 could be alternatively prepared by heating a toluene solution of isolated 3 (vide inf ra) in the presence of 4 Å molecular sieves in a high yield (Scheme 4). Figure 3. Molecular structure of the complex 2 drawn with 30% probability ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−B1 2.517(5), Ru1−C1 2.289(4), Ru1−C2 2.204(4), Ru1−C3 2.220(4), Ru1−C4 2.260(4), Ru1−C5 2.331(4), B1−O1 1.378(6), Ru1−Cl1 2.4451(12), Ru1−P1 2.3507(12), Ru1−P2 2.3579(12), Ru2−B2 2.546(5), Ru2−C6 2.295(5), Ru2−C7 2.230(4), Ru2−C8 2.225(5), Ru2−C9 2.203(4), Ru2−C10 2.290(4), B2−O1 1.388(6), Ru2−Cl2 2.4358(11), Ru2−P3 2.3336(12), Ru2−P4 2.3585(11); P1−Ru1−P2 98.83(4), P1−Ru1− Cl1 92.80(4), P2−Ru1−Cl1 90.44(4), B1−O1−B2 130.9(4), P3− Ru2−P4 98.22(4), P3−Ru2−Cl2 90.38(4), P4−Ru2−Cl2 92.28(4).

Scheme 4. Interconversion of 1a, 1b, 2, and 3 through Nucleophilic Substitution Reactions

them, probably to reduce the repulsive interaction. As reflected by the structural parameters of the B−O−B moiety, the oxygen atom is also sp2 hybridized, and the three-centered π interaction over the B−O−B unit can still be expected to some extent, but obviously weaker than the B−O π overlap in 1a and 1b. The NMR spectroscopic data of 2 were fully consistent with the solid structure. The 31P{1H} NMR spectrum showed one singlet at 30.4 ppm. In the 1H NMR, the five protons on the boratabenzene ring displayed three resonances at 5.30 (dd, 3 J(HH) = 8.6, 5.3 Hz, 2H, BCHCH), 4.30 (t, 3J(HH) = 5.3 Hz, 1H, BCHCHCH), and 2.62 ppm (d, 3J(HH) = 8.6 Hz, 2H, BCH) in a ratio of 2:1:2. In the 13C{1H} NMR, the three kinds of ring carbon signals for the boratabenzene ligand were observed at 109.5 (s, BCHCH), 75.9 (br, BCH), and 74.4 ppm (br, BCHCHCH). Isolation of the oxo-bis(boratabenzene) bridged dinuclear ruthenium complex 2 is interesting. Scheme 3 shows the plausible pathway for the formation of 2. Initially, nucleophilic addition of water to C5H5BPPh3 could provide the 1hydroxyboracyclohexa-2,4-diene species 2A. Analogous addition of alcohols to C5H5BPMe3 to give related 1-alkoxybora-

Complexes 1a, 1b, and 2 can be stored in the solid form under an inert atmosphere for at least 1 week without appreciable decomposition. However, they are extraordinarily sensitive to air and moisture in solution. When a THF solution of 1a, 1b, or 2 was left to stand at room temperature in an NMR tube, a small amount of the new species precipitated out gradually. X-ray diffraction study demonstrates that the new species was the B-hydroxy boratabenzene complex (η6-C5H5BOH)RuCl(PPh3)2 (3). As shown in Figure 4, complex 3 has a structure similar to those of 1a and 1b, with the OR group bound to the boron atom replaced by OH. The hydroxyl group is likely derived from the moisture leakage into the NMR tube. Thus, treatment of a THF solution of 1a, 1b, or 2 with excess water at room temperature for 48 h or at 85 °C for 8 h produced complex 3 exclusively, which was isolated in 90% yield (Scheme 4). Of note, when 1a or 1b was treated with a smaller amount of water (1:10), the reaction produced a mixture of 2 and 3. Complex 3 has also been well-characterized by NMR as well as elemental analysis. In the 1H NMR spectrum, the proton signal for the BOH was observed at 2.30 ppm as a broad peak. Apparently, complex 3 was formed via nucleophilic substitution at the boron atom of the boratabenzene ligand in complexes 1a, 1b, or 2, which is a well-known type of reaction and has been established as a versatile and general method for the synthesis of various boratabenzene complexes.23 Interestingly, complexes 2 and 3 could, in turn, react readily with excess EtOH or MeOH in THF to yield the corresponding B-alkoxy products 1a and 1b, respectively. As a result, the interconversion of complexes 1a, 1b, 2, and 3 can be achieved on the basis of this nucleophilic substitution reaction.

Scheme 3. Proposed Mechanism for the Formation of Complex 2

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Organometallics

state after being heated for an additional 36 h, and the 31 1 P{ H}NMR spectrum showed signals of 1a and the two new species in about a ratio of 1:1.5:1, as was also the case when the reaction was performed using a larger excess of phenylacetylene. Further prolonged heating of the reaction mixture led to the decomposition of the two species, and the reaction became messy. It should be noted that the reactions of Cp*RuCl(PPh3)2 with terminal alkynes, including phenylacetylene, have been reported to produce the neutral monophosphine vinylidene complex Cp*RuCl(CCHR)(PPh3) (R = Ph, But, SiMe3) very easily by displacement of one PPh3 ligand.25 A common requirement for the formation of a vinylidene complex from the reaction of a terminal alkyne with a transition-metal complex is the initial binding of the alkyne on the metal center to form an η2-alkyne complex, which then isomerizes to vinylidene.7g,24 We thus speculated that the above-mentioned broadened singlet at 35.1 ppm and the singlet at 48.0 ppm in the 31P{1H} NMR spectrum might be attributed to the related π-alkyne complex (η6-C5H5BOEt)RuCl(HCCPh)(PPh3) and vinylidene complex (η6-C5H5BOEt)RuCl(CCHPh)(PPh3), respectively. Unfortunately, our efforts to isolate the two new species from the reaction mixture was unsuccessful, and further attempt to provide supporting evidence for the formation of the π-alkyne and the vinylidene species from the in situ 1H NMR was hampered by the wide range of the 1H NMR signals for the boratabenzene ring protons (ca. 6.20−1.90 ppm) and the presence of three boratabenzene-containing species in the solution. It has been established that the conversion of alkynes into their vinylidene tautomers is facilitated in electron-rich transition-metal complexes.7g,24e We reasoned that the isomerization of terminal alkyne to vinylidene will be more difficult for 1a than Cp*RuCl(PPh3)2 due to the weaker donation ability of the boratabenzene ligand as compared to Cp*. On the other hand, dissociation of a PPh3 ligand is expected to be more difficult for 1a than Cp*RuCl(PPh3)2 because the boratabenzene ligand C5H5BOEt is less bulky than Cp* (vide supra). Besides, the dissociated PPh3 ligand present in the solution could re-coordinate to the metal center in competition with the alkyne coordination, which may furnish an equilibrium between 1a, the η2-alkyne, and the vinylidene species in the solution, and thus inhibit further reaction. It is also noteworthy that the neutral monophosphine complex CpRuCl(CCHR)(PPh3) has not been reported, presumably for reasons similar to those stated above. By contrast, the vinylidene complex CpRuCl( CCHPh){PPh2(2-MeC6H4)} was reported to be prepared conveniently from the reaction of CpRuCl{PPh2(2-MeC6H4)}2 with phenylacetylene under mild conditions, which is favored by the facile dissociation of one of the bulkier phosphine ligands.26 Moreover, the complex CpRuCl{PPh2(2-MeC6H4)}2 has been observed to react with the internal alkyne MeO2CC CCO2Me, resulting in an equilibrium with the π-alkyne complex CpRuCl(η 2 -MeO 2 CCCCO 2 Me){PPh 2 (2MeC6H4)} in solution.26 On the other hand, ruthenium vinylidene complexes could react smoothly with weak nucleophiles such as alcohols to give Fischer carbene complexes of the type LnRuC(OR′)CH2R, due to the electrophilic nature of the vinylidene α-carbon.27 In this context, it is reasonable to envision that, when a terminal alkyne bearing a tethered hydroxyl group is used to react with 1a, the corresponding vinylidene intermediate thus generated can undergo further transformation by an intramolecular nucleophilic attack of the hydroxyl group at the α-carbon, so

Figure 4. Molecular structure of the complex 3 drawn with 30% probability ellipsoids. Hydrogen atoms except that of the hydroxyl group are omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−B1 2.543(3), Ru1−C1 2.306(3), Ru1−C2 2.240(2), Ru1−C3 2.233(2), Ru1−C4 2.221(3), Ru1−C5 2.278(3), B1−O1 1.383(4), Ru1−P1 2.3504(8), Ru1−P2 2.3279(9), Ru1−Cl1 2.4332(10); P1−Ru1−P2 98.08(3), P1−Ru1−Cl 1 93.68(3), P2− Ru1−Cl1 88.74(4).

Reactivity of Complex 1a toward Phenylacetylene and Terminal ω-Alkynols. Half-sandwich ruthenium complexes exhibit diversified reactivity toward terminal alkynes,6c,d which has been extensively exploited in a broad spectrum of catalytic transformations.7b−i,8a−f,h−n Many of these processes involve the conversion of a terminal alkyne to a vinylidene ligand.6c−e,7d,h,8a,b,f,i−n,24 Since the complexes we obtained above are the first examples of half-sandwich boratabenzene ruthenium complexes, we are, of course, interested in their reactivity toward terminal alkynes. Initially, we investigated the reaction of 1a with phenylacetylene. As monitored by in situ NMR, no reaction could be observed when a solution of 1a and phenylacetylene (1:10) in C6D6 was allowed to stand for 8 h. Upon heating at 85 °C, the reaction of 1a with phenylacetylene did occur. After 12 h, the 31 1 P{ H}NMR spectrum showed signals of the liberated PPh3 and the starting material 1a (∼50%), as well as a broadened singlet at 35.1 ppm and a singlet at 48.0 ppm for two newly formed species (Figure 5). The signals of the two new species grew up gradually in further reaction, accompanied by the relevant consumption of the starting material 1a. However, the reaction could not be completed and seemed to reach a steady

Figure 5. Time-evolved 31P{1H} NMR spectra for the reaction of complex 1a with phenylacetylene in C6D6 at 85 °C. E


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Organometallics that the reaction equilibrium mentioned above can be drawn to the formation of the vinylidene and thus facilitate the reaction going on. In fact, several reactions of ruthenium complexes with terminal ω-alkynols to give cyclic oxacarbene ruthenium complexes have been reported.27a,28 Moreover, oxacyclocarbene ruthenium complexes are relevant to the ruthenium-catalyzed endo cycloisomerization of terminal ω-alkynols.28i,29 Accordingly, we have investigated the reactions of 1a with terminal ωalkynols. Indeed, the reaction of 1a with 3 equiv of but-3-yn-1-ol in toluene proceeded smoothly at 85 °C to produce the fivemembered oxacyclocarbene ruthenium complex (η6-C5H5BOEt)RuCl(CCH2CH2CH2O)(PPh3) (4) cleanly within 24 h, which was isolated as a yellow solid in 78% yield (Scheme 5). Complex 1a is also reactive toward 4-pentyn-1-ol,

Figure 6. Molecular structure of the complex 4 drawn with 30% probability ellipsoids. Hydrogen atoms except those of the cyclic oxacarbene ring are omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−Cl1 2.4295(14), Ru1−P1 2.3159(14), Ru1− C11 1.938(5), Ru1−B1 2.454(6), Ru1−C1 2.249(5), Ru1−C2 2.213(5), Ru1−C3 2.279(5), Ru1−C4 2.269(5), Ru1−C5 2.302(5), B1−O1 1.386(7), O1−C6 1.439(7), C(11)−O(2) 1.316(4), C(11)− C(12) 1.508(4), C(12)−C(13) 1.530(5), C(13)−C(14) 1.504(5), C(14)−O(2) 1.489(4); P1−Ru1−Cl1 92.59(5), P1−Ru1−C11 90.00(14), Cl1−Ru1−C11 89.69(14), B1−O1−C(6) 118.2(4).

Scheme 5. Reactions of 1a with 3-Butyn-1-ol and 4-Pentyn1-ol

but a longer reaction time was needed to complete the reaction, as indicated by the in situ 31P{1H} NMR. Thus, under similar conditions, heating a mixture of 1a and 4-pentyn-1-ol in toluene for 36 h afforded the corresponding six-membered cyclic oxacarbene complex (η6-C5H5BOEt)RuCl(CCH2CH2CH2CH2O)(PPh3) (5) in 70% isolated yield (Scheme 5). The relatively slower reaction for the latter can be rationalized in terms of a lesser tendency for the intramolecular nucleophilic attack of the hydroxyl group at the α-carbon atom of the vinylidene intermediate, as a result of a higher flexibility of the longer hydroxyalkyl substituent combined with a lower thermal stability of the vinylidene intermediate.28f,30 The structure of 4 has been established by an X-ray diffraction study. Yellow single crystals were obtained via slow diffusion of n-hexane into a CH2Cl2 solution of 4. The molecular structure shows the typical three-legged piano stool geometry around the ruthenium atom, with a five-membered cyclic oxacarbene ligand located below the exocyclic ethoxyl group of the boratabenzene ligand together with one Cl ligand and one PPh3 ligand as the three legs (Figure 6). As a consequence, the molecule possesses a chiral center at the ruthenium atom, while the complex was obtained as a racemic mixture and crystallized in the centric space group P1̅. The Ru(1)−C(11) bond distance of 1.938(5) Å is comparable to those reported for other oxacyclocarbene ruthenium complexes.28 The C11−O2 and C11−C12 bond lengths (1.316(4) and 1.508(4) Å, respectively) of the cyclic oxacarbene ligand in 4 also agree well with those reported for the related complexes.28 Both complexes 4 and 5 have been well-characterized by NMR spectroscopy as well as elemental analysis. The 31P{1H} NMR spectra showed a singlet at 45.9 ppm for 4 and at 47.2 ppm for 5. Due to the chirality at the metal center, the two protons at each of the two ortho or meta positions of the boratabenzene ligand become inequivalent, thus the 1H NMR spectra showed five resonances for the boratabenzene ring protons, which were observed at 6.25, 5.70, 4.60, 3.91, and 1.97

ppm for 4, and 6.20, 5.53, 4.68, 3.96, and 1.89 ppm for 5. Likewise, five kinds of 13C{1H} NMR signals were observed for the ring carbons of each boratabenzene ligand. And also, the two protons of each methylene group of the oxacyclocarbene ring are diastereotopic, giving rise to complicated 1H NMR spectra with three pairs of multiplet signals in the aliphatic region between 1.57 and 4.72 ppm in the case of 4 and four pairs of signals between 1.42 and 4.44 ppm in the case of 5, similar to what was reported for other chiral ruthenium oxacyclocarbene complexes.27a,28f−h The presence of the carbene ligand was supported by the low-filed doublets at 319.1 (2J(CP) = 18.7 Hz) and 326.0 ppm (2J(CP) = 18.9 Hz) in the 13C{1H} NMR spectra, corresponding to the RuC resonances for 4 and 5, respectively.28 The 13C{1H} signals for the remaining carbons of the oxacyclocarbene ligand were observed at 21.8, 59.3, and 83.2 ppm for 4, and at 17.3, 21.5, 53.4, and 75.0 ppm for 5. We also carried out the reaction of 1a with racemic pent-4yn-2-ol. As can be expected, due to the presence of a chiral carbon center in the alkynol, the corresponding cyclic oxacarbene complex thus formed should contain two stereogenic centers, at the ruthenium center and the chiral carbon, respectively. Thus, the reaction of 1a with racemic pent-4-yn-2ol resulted in the formation of the five-membered 3-methyl-2oxacyclopentylidene complex (η6-C5H5BOEt)RuCl(CCH2CH2CH(Me)O)(PPh3) (6), existing as a pair of diasteromers 6a and 6b in a ratio of 1:0.8 (Scheme 6). The existence of the two isomers is supported by the two sets of characteristic Scheme 6. Reaction of 1a with Racemic Pent-4-yn-2-ol

F


Article

Organometallics

the weaker donor boratabenzene ligand can generate more electrophilic metal center, which then facilitate the nucleophilic attack at the neutral vinylidene intermediate leading to the formation of the neutral monophosphine ruthenium oxacyclocarbene complexes 4−6.

signals observed for the product in the NMR spectra. In particular, the 31P{1H} NMR spectrum shows two RuPPh3 signals at 46.1 and 46.4 ppm (in CDCl3), and the 13C{1H} spectrum (in CD2Cl2) displays two characteristic RuC signals at 317.4 (d, 2J(CP) = 18.4 Hz) and 317.6 (d, 2J(CP) = 18.1 Hz) ppm for the major and minor isomers, respectively. Two sets of proton signals for the boratabenzene and the oxacyclocarbene ligands are also evident in the 1H NMR spectrum. Our attempt to separate the two isomers from each other in pure form failed finally. Fortunately, the molecular structure of one of the isomers has been confirmed by X-ray diffraction. Crystals of 6a suitable for X-ray diffraction were grown from a dichloromethane solution of a mixture of 6a and 6b layered with n-hexane. A view of the molecular geometry of 6a is shown in Figure 7, which clearly indicates that complex 6a has a

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CONCLUSIONS We have described the synthesis of the first examples of halfsandwich boratabenzene ruthenium complexes, including the Balkoxy and B-hydroxy complexes (η6-C5H5BOR)RuCl(PPh3)2 (R = Et, 1a; Me, 1b; H, 3), as well as the dinuclear complex (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2) with an oxobis(boratabenzene) bridging ligand connected by the B−O−B linkage. All these complexes have been well-characterized. Meanwhile, complexes 1a, 1b, 2, and 3 could interconvert into each other through nucleophilic substitution reactions at the boron atom on the boratabenzene ligand. Unlike the cyclopentadienyl-based analogues Cp*RuCl(PPh 3 ) 2 and CpRuCl{PPh2(2-MeC6H4)}2, preliminary study on the reactivity of 1a with phenylacetylene showed that the reaction did not afford the expected neutral vinylidene complex successfully, presumably due to the weaker donating property of the boratabenzene ligand combined with the difficult dissociation of the PPh3 ligand. Whereas 1a reacted with terminal ωalkynols HCC(CH2)nCH(R)OH (R = H, n = 1, 2; R = Me, n = 1) to provide the neutral oxacyclocarbene complexes (η6C5H5BOEt)RuCl(CCH2CH2CH2O)(PPh3) (4), (η6-C5H5BOEt)RuCl(CCH2CH2CH2CH2O)(PPh3) (5), and (η6C 5 H 5 BOEt)RuCl(CCH 2 CH 2 CH(Me)O)(PPh 3 ) (6) smoothly. Similar reactions have not been reported for the analogous neutral cyclopentadienyl-based ruthenium system. Probably the more electrophilic ruthenium center in borarabenzene complex 1a could in turn facilitate the intramolecular nucleophilic attack at the neutral vinylidene intermediate to give the rare examples of neutral monophosphine ruthenium oxacyclocarbene complexes 4−6. Further studies directed toward the synthesis of various half-sandwich boratabenzene ruthenium complexes and the investigations on their reactivity are currently underway in our laboratory.

Figure 7. Molecular structure of the complex 6a drawn with 30% probability ellipsoids. Hydrogen atoms except those of the cyclic oxacarbene ring are omitted for clarity. Selected bond distances (Å) and angles (deg): Ru1−Cl1 2.4256(9), Ru1−P1 2.2975(10), Ru1− C11 1.934(3), Ru1−B1 2.424(4), Ru1−C1 2.306(3), Ru1−C2 2.266(3), Ru1−C3 2.269(3), Ru1−C4 2.202(3), Ru1−C5 2.242(3), B1−O1 1.389(4), O1−C6 1.427(4), C(11)−O(2) 1.330(4), C(11)− C(12) 1.501(5), C(12)−C(13) 1.510(4), C(13)−C(14) 1.467(5), C(14)−O(2) 1.495(4); P1−Ru1−Cl1 92.60(4), P1−Ru1−C11 90.93(11), Cl1−Ru1−C11 92.18(10), B1−O1−C6 118.8(3).

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EXPERIMENTAL SECTION

General Methods. All manipulations were carried out under an inert atmosphere (N2) by means of standard Schlenk techniques and a glovebox unless otherwise stated. Solvents were distilled from sodium/ benzophenone (toluene, tetrahydrofuran, Et2O, n-hexane) or calcium hydride (CH2Cl2, CHCl3) under N2 prior to use. The starting material of RuCl2(PPh3)3,31 1-chloro-2-(trimethylsilyl)boracyclohexa-2,5-diene,16a C5H5BPMe3,16a Na[C5H5BOEt],16b and Na[C5H5BOMe]16b were prepared according to the literature methods. Other reagents were used as received from commercial sources without further purification. NMR spectroscopic experiments were carried out on a Bruker AV400, Bruker AV500, or Bruker AV850 spectrometer. 1H and 13 C{1H} NMR chemical shifts are relative to TMS, and 31P{1H} NMR and 11B{1H} NMR are relative to 85% H3PO4 and BF3·Et2O as the external standard, respectively. Elemental analyses data were obtained on an Elementar Analysensysteme GmbH Vario EL III instrument. Preparation and Characterization of C5H5BPPh3 (Bb−PPh3). The borabenzene (Bb)−PPh3 complex was prepared by a similar procedure reported for the preparation of Bb-PMe3.16 PPh3 (245 mg, 0.95 mmol) and 1-chloro-2-(trimethylsilyl)boracyclohexa-2,5-diene (372 mg, 0.95 mmol)15 were mixed in n-hexane (15 mL) and then stirred to result in an exothermic reaction and the precipitation of a white solid. The reaction was stirred for another 8 h, during which time additional white solid precipitated from the reaction mixture. The solution was decanted, and the remaining solids were washed with n-

similar structure to that of 4. The Ru1−C11, C11−O2, and C11−C12 bond distances (1.934(3), 1.330(4), and 1.501(5) Å, respectively) are fully consistent with those of 4. Again, as was the case in the structure of 4, the five-membered cyclic oxacarbene ligand is located below the ethoxyl substituent of the boratabenzene ligand. The Me group on the five-membered ring is oriented away from the exocyclic OEt group to minimize the steric interaction. Although a number of ruthenium oxacyclocarbene complexes have been reported, most of the examples reported so far are cationic complexes, except for two recent examples.28h,i For instance, several reactions of cationic Cp or substituted Cp ruthenium complexes with ω-alkynols have been reported to give the cationic bis-phosphine oxacyclocarbene complexes.28a−c,f However, no examples exist in the literature concerning the neutral monophosphine complexes in cyclopentadienyl-based ruthenium system. This situation can be understandable considering the fact that cationic vinylidene intermediates will be more favored for the nucleophilic attack at the α-carbon atom. While in the reactions of 1a, presumably G


Article

Organometallics hexane (2 × 5 mL) and then dried under vacuum. Yield: 270 mg, 84%. 1 H NMR (400.1 MHz, CDCl3): δ 7.66 (m, 6H, Ph), 7.56 (m, 3H, Ph), 7.47 (m, 6H, Ph), 7.33 (br, 2H, BCH), 7.05 (t, 3J(HH) = 8.6 Hz, 2H, BCHCH), 6.92 (t, 3J(HH) = 7.2 Hz, 1H, BCHCHCH). 31P{1H} NMR (162.0 MHz, CDCl3): δ 5.77 (dbr, 1J(PB) = 118.8 Hz, BPPh3). 13 C{1H} NMR (100.6 MHz, CDCl3): δ 137.7−127.1(m, PPh3), 133.7 (s, BCHCHCH), 126.9 (s, BCHCH), 120.0 (br, BCH). 11B{1H} NMR (128.4 MHz, CDCl3): δ 34.2 (br). Preparation and Characterization of Complex (η6-C5H5BOEt)RuCl(PPh3)2 (1a). Method A: A mixture of RuCl2(PPh3)3 (1.0 g, 0.95 mmol) and Na[C5H5BOEt] (157 mg, 1.09 mmol) in toluene (30 mL) was stirred at 85 °C for about 4 h to give an orange solution. The brown residue was removed by filtration, and the filtrate was concentrated to a volume of approximately 3 mL. Subsequent addition of n-hexane (20 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with n-hexane (2 × 10 mL) and diethyl ether (2 × 10 mL), and then dried under vacuum. Yield: 625 mg, 84%. Method B: CH3CH2OH (0.2 mL, 3.43 mmol) was added to a solution of (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2) (200 mg, 0.13 mmol) in tetrahydrofuran (5 mL). The reaction mixture was stirred under reflux for about 4 h to give a yellow solution. The volume of the solution was reduced to approximately 1 mL under vacuum. Addition of n-hexane (10 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with n-hexane (2 × 5 mL) and diethyl ether (2 × 5 mL), and then dried under vacuum. Yield: 188 mg, 90%. Method C: CH3CH2OH (0.1 mL, 1.71 mmol) was added to a solution of (η6-C5H5BOH)RuCl(PPh3)2 (3) (200 mg, 0.26 mmol) in tetrahydrofuran (5 mL). The reaction mixture was stirred under reflux for about 4 h to give a yellow solution. The volume of the solution was reduced to approximately 1 mL under vacuum. Addition of n-hexane (5 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with n-hexane (2 × 5 mL) and diethyl ether (2 × 3 mL), and then dried under vacuum. Yield: 176 mg, 85%. 1H NMR (400.1 MHz, C6D6): δ 7.70−6.63 (m, 30H, PPh3), 5.26 (dd, 3J(HH) = 8.1, 5.2 Hz, 2H, BCHCH), 3.87 (t, 3J(HH) = 5.0 Hz, 1H, BCHCHCH), 2.98 (d, 3J(HH) = 8.2 Hz, 2H, BCH), 3.31 (br, 2H, BOCH2), 1.08 (t, 3J(HH) = 7.0 Hz, 3H, BOCH2CH3). 31 1 P{ H} NMR (162.0 MHz, C6D6): δ 30.7 (s, RuPPh3). 13C{1H} NMR (100.6 MHz, C6D6): δ 138.2−127.4 (m, PPh3), 108.4 (s, BCHCH), 73.2 (br, BCH), 72.7 (br, BCHCHCH), 60.3 (s, BOCH2), 17.6 (s, BOCH2CH3). 11B{1H} NMR (128.4 MHz, C6D6): δ 21.2 (br). Anal. Calcd for C43H40BOClP2Ru: C 66.04; H 5.16. Found: C 66.24; H 5.20. Preparation and Characterization of Complex (η6-C5H5BOMe)RuCl(PPh3)2 (1b). Method A: A mixture of RuCl2(PPh3)3 (1.0 g, 0.95 mmol) and Na[C5H5BOMe] (154 mg, 1.09 mmol) in toluene (30 mL) was stirred at 85 °C for about 4 h to give an orange solution. The brown residue was removed by filtration, and the filtrate was concentrated to a volume of approximately 3 mL. Subsequent addition of n-hexane (20 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with n-hexane (2 × 10 mL) and diethyl ether (2 × 10 mL), and then dried under vacuum. Yield: 575 mg, 77%. Method B: MeOH (0.2 mL, 4.95 mmol) was added to a solution of (μ2-η6,η6-C5H5BOBC5H5)[RuCl(PPh3)2]2 (2) (200 mg, 0.132 mmol) in tetrahydrofuran (5 mL). The reaction mixture was stirred under reflux for about 4 h to give a yellow solution. The volume of the solution was reduced to approximately 1 mL under vacuum. Addition of n-hexane (10 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with nhexane (2 × 5 mL) and diethyl ether (2 × 5 mL), and then dried under vacuum. Yield: 184 mg, 90%. Method C: MeOH (0.1 mL, 2.46 mmol) was added to a solution of (η6-C5H5BOH)RuCl(PPh3)2 (3) (200 mg, 0.265 mmol) in tetrahydrofuran (5 mL). The reaction mixture was stirred under reflux for about 4 h to give a yellow solution. The volume of the solution was reduced to approximately 1 mL under vacuum. Addition of n-hexane (5 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with nhexane (2 × 5 mL) and diethyl ether (2 × 3 mL), and then dried under vacuum. Yield: 166 mg, 82%. 1H NMR (400.1 MHz, C6D6): δ 7.50−7.12 (m, 30H, PPh3), 5.26 (dd, 3J(HH) = 9.0 Hz, 5.0 Hz, 2H,

BCHCH), 3.83 (t, 3J(HH) = 5.0 Hz, 1H, BCHCHCH), 3.01 (d, J(HH) = 9.0 Hz, 2H, BCH), 3.27 (br, 3H, BOCH3). 31P{1H} NMR (162.0 MHz, C6D6): δ 30.5 (s, RuPPh3). 13C{1H} NMR (100.6 MHz, C6D6): δ 137.3−127.4 (m, PPh3), 107.6 (s, BCHCH), 72.2 (br, BCH), 72.0 (br, BCHCHCH), 52.9 (s, BOCH3). 11B{1H} NMR (128.4 MHz, C6D6): δ 21.6 (br). Anal. Calcd for C42H38BOClP2Ru: C 65.68; H 4.99. Found: C 66.00; H 5.27. Preparation and Characterization of Complex (μ2-η6,η6C5H5BOBC5H5)[RuCl(PPh3)2]2 (2). Method A: A mixture of RuCl2(PPh3)3 (1.0 g, 0.95 mmol) and C5H5BPPh3 (372 mg, 0.95 mmol) in tetrahydrofuran (30 mL) was stirred under reflux for about 4 h to give an orange suspension. The yellow solid suspension was collected by filtration, which was washed with n-hexane (2 × 10 mL) and diethyl ether (2 × 10 mL), and then dried under vacuum. Yield: 625 mg, 84%. Method B: A mixture of (η6-C5H5BOH)RuCl(PPh3)2 (3) (200 mg, 0.26 mmol) and 4 Å molecular sieves (200 mg) in toluene (5 mL) was stirred at 85 °C for about 3 h. The reaction solution was filtered, and the filtrate was concentrated to a volume of approximately 1 mL under vacuum. Addition of n-hexane (5 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with nhexane (2 × 10 mL) and diethyl ether (2 × 5 mL), and then dried under vacuum. Yield: 176 mg, 90%. 1H NMR (400.1 MHz, CD2Cl2): δ 7.40−7.02 (m, 30H, PPh3), 5.30 (dd, 3J(HH) = 8.6, 5.3 Hz, 2H, BCHCH), 4.30 (t, 3J(HH) = 5.3 Hz, 1H, BCHCHCH), 2.62 (d, 3 J(HH) = 8.6 Hz, 2H, BCH). 31P{1H} NMR (162.0 MHz, CD2Cl2): δ 30.4 (s, RuPPh3). 13C{1H} NMR (100.6 MHz, CD2Cl2): δ 137.7− 127.1(m, PPh3), 109.5 (s, BCHCH), 75.9 (br, BCH), 74.4 (br, BCHCHCH). 11B{1H} NMR (128.4 MHz, CD2Cl2): δ 22.2 (br). Anal. Calcd for C82H70B2OCl2P4Ru2: C 66.10; H 4.74. Found: C 66.24; H 5.08. Preparation and Characterization of Complex (η6-C5H5BOH)RuCl(PPh3)2 (3). Method A: H2O (0.1 mL, 5.56 mmol) was added to a solution of (η6-C5H5BOEt)RuCl(PPh3)2 (1a) (200 mg, 0.25 mmol) in tetrahydrofuran (5 mL). The reaction mixture was stirred under reflux for about 8 h to give a yellow solution. The volume of the solution was reduced to approximately 0.5 mL under vacuum. Addition of n-hexane (5 mL) to the residue produced a yellow precipitate. The yellow solid was washed with n-hexane (2 × 5 mL) and diethyl ether (2 × 3 mL) and then dried under vacuum. Yield: 179 mg, 90%. Method B: H2O (0.1 mL, 5.56 mmol) was added to a solution of (μ2-η6,η6C5H5BOBC5H5)[RuCl(PPh3)2]2 (2) (200 mg, 0.13 mmol) in tetrahydrofuran (5 mL). The reaction mixture was stirred under reflux for about 8 h to give a yellow solution. The volume of the solution was reduced to approximately 1 mL under vacuum. Addition of n-hexane (5 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with n-hexane (2 × 5 mL) and diethyl ether (2 × 3 mL), and then dried under vacuum. Yield: 176 mg, 89%. 1H NMR (400.1 MHz, CD2Cl2): δ 7.50−7.12 (m, 30H, PPh3), 5.41 (dd, 3J(HH) = 8.1 Hz, 5.2 Hz, 2H, BCHCH), 4.17 (t, 3 J(HH) = 5.0 Hz, 1H, BCHCHCH), 2.86 (d, 3J(HH) = 8.2 Hz, 2H, BCH), 2.30 (br, 1H, OH). 31P{1H} NMR (162.0 MHz, CD2Cl2): δ 30.6 (s, RuPPh3). 13C{1H} NMR (100.6 MHz, CD2Cl2): δ 138.5− 127.0 (m, PPh3), 110.0 (s, BCHCH), 75.0 (br, BCHCHCH), 73.5 (br, BCH). 11B{1H} NMR (128.4 MHz, CD2Cl2): δ 22.0 (br). Anal. Calcd for C41H36BOClP2Ru: C 65.31; H 4.81. Found: C 65.24; H 5.20. Preparation and Characterization of Complex (η6-C5H5BOEt)RuCl(CCH2CH2CH2O)(PPh3) (4). A mixture of (η6-C5H5BOEt)RuCl(PPh3)2 (1a) (400 mg, 0.51 mmol) and but-3-yn-1-ol (116 μL, 1.53 mmol) in toluene (30 mL) was stirred at 85 °C for about 24 h to give an orange suspension. The volume of the solution was reduced to approximately 1 mL under vacuum. Subsequent addition of nhexane (10 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with n-hexane (2 × 10 mL) and diethyl ether (2 × 5 mL), and then dried under vacuum. Yield: 235 mg, 78%. 1H NMR (400.1 MHz, CDCl3): δ 7.56−7.29 (m, 15H, PPh3), 6.25 (dd, 3J(HH) = 10.2, 6.1 Hz, 1H, BCHCH), 5.70 (dd, 3 J(HH) = 6.0, 5.3 Hz, 1H, BCHCHCH), 4.60 (dd, 3J(HH) = 7.7, 5.2 Hz, 1H, BCHCH), 3.91 (d, 3J(HH) = 10.2 Hz, 1H, BCH), 1.97 (d, 3 J(HH) = 7.7 Hz, 1H, BCH), 3.68 (m, 2H, BOCH2), 1.17 (t, 3J(HH) = 7.0 Hz, 3H, BOCH2CH3), 4.72 (m, 1H, RuCOCH2), 3.86 (m, 1H, 3

H


Article

Organometallics

CD2Cl2): δ 32.0 (br). Anal. Calcd for C30H33BO2ClPRu: C 59.67; H 5.51. Found: C 59.84; H 5.42. Crystallograhic Analysis. Data collections were performed on an Oxford Gemini S Ultra or a Rigaku R-AXIS SPIDER IP CCD area detector using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å). Multiscan absorption corrections (SADABS) were applied. All of the data were corrected for absorption effects using the multiscan technique. The structures were solved by direct methods, expanded by difference Fourier syntheses, and refined by full-matrix least-squares on F2 using the Bruker SHELXTL-97 program package. Non-H atoms were refined anisotropically unless otherwise stated. Hydrogen atoms were introduced at their geometric positions and refined as riding atoms. Crystals suitable for X-ray diffraction were grown from a CH2Cl2 (1a, 2, 4, 6a), CHCl3 (1b), or tetrahydrofuran (3) solution layered with n-hexane. CCDC-1033717 (1a), CCDC1033718 (1b), CCDC-1046734 (2), CCDC-1033719 (3), CCDC1033720 (4), and CCDC-1033727 (6a) contain the crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif.

RuCOCH2), 3.91 (m, 1H, RuCCH2), 3.44 (m, 1H, RuCCH2), 1.90 (m, 1H, RuCOCH2CH2), 1.57 (m, 1H, RuCOCH2CH2). 31P{1H} NMR (162.0 MHz, CDCl3): δ 45.9 (s, RuPPh3). 13C{1H} NMR (100.6 MHz, CDCl3): δ 319.1 (d, 2J(PC) = 18.7 Hz, RuC), 135.1− 127.9 (m, PPh3), 121.3 (s, BCHCH), 78.6 (s, BCHCHCH), 104.6 (s, BCHCH), 72.0 (br, BCH), 56.4 (br, BCH), 60.5 (s, BOCH2), 17.4 (s, BOCH2CH3), 83.2 (s, RuCOCH2), 59.3 (s, RuCCH2), 21.8 (s, RuCOCH2CH2). 11B{1H} NMR (128.4 MHz, CD2Cl2): δ 24.6 (br). Anal. Calcd for C29H31BO2ClPRu: C 59.05; H 5.30. Found: C 59.07; H 5.80. Preparation and Characterization of Complex (η6-C5H5B OEt)RuCl(CCH2CH2CH2CH2O)(PPh3) (5). A mixture of (η6C5H5BOEt)RuCl(PPh3)2 (1a) (400 mg, 0.51 mmol) and pent-4-yn1-ol (143 μL, 1.53 mmol) in toluene (30 mL) was stirred at 85 °C for about 36 h to give an orange suspension. The volume of the solution was reduced to approximately 1 mL under vacuum. Subsequent addition of n-hexane (10 mL) to the residue produced a yellow precipitate, which was collected by filtration, washed with n-hexane (2 × 10 mL) and diethyl ether (2 × 5 mL), and then dried under vacuum. Yield: 215 mg, 70%. 1H NMR (500.1 MHz, CDCl3): δ 7.53−7.34 (m, 15H, PPh3), 6.20 (dd, 3J(HH) = 9.7, 5.1 Hz, 1H, BCHCH), 5.53 (t, 3 J(HH) = 4.9 Hz, 1H, BCHCHCH), 4.68 (dd, 3J(HH) = 8.4, 4.9 Hz, 1H, BCHCH), 3.96 (d, 3J(HH) = 9.7 Hz, 1H, BCH), 1.89 (d, 3J(HH) = 8.4 Hz, 1H, BCH), 3.74(dq, 3J(HH) = 7.0, 3.0 Hz, 2H, BOCH2), 1.22 (t, 3J(HH) = 7.0 Hz, 3H, BOCH2CH3), 4.44 (dq, 3J(HH) = 10.9, 5.4 Hz, 1H, RuCOCH2), 3.56 (dq, 3J(HH) = 11.0, 4.5 Hz, 1H, RuCOCH2), 4.28 (dt, 3J(HH) = 19.4, 5.7 Hz, 1H, RuCCH2), 3.38 (dt, 3 J(HH) = 19.5, 7.6 Hz, 1H, RuCCH2), 1.78 (m, 1H, RuCOCH2CH2), 1.28 (m, 1H, RuCOCH2CH2), 1.68 (m, 1H, RuCCH2CH2), 1.42 (m, 1H, RuCCH2CH2). 31P{1H} NMR (202.5 MHz, CDCl3): δ 47.2 (s, RuPPh3). 13C{1H} NMR (125.8 MHz, CDCl3): δ 326.0 (d, 2J(PC) = 18.9 Hz, RuC), 135.4−127.9 (m, PPh3), 121.8 (s, BCHCH), 77.7 (s, BCHCHCH), 105.0 (s, BCHCH), 72.9 (br, BCH), 56.2 (br, BCH), 60.6 (s, BOCH2), 17.5 (s, BOCH2CH3), 75.0 (s, RuCOCH2), 53.4 (s, RuCCH2), 21.5 (s, RuCOCH2CH2), 17.3 (RuCCH2CH2). 11B{1H} NMR (128.4 MHz, CDCl 3): δ 35.1 (br). Anal. Calcd for C30H33BO2ClPRu: C 59.67; H 5.51. Found: C 59.92; H 5.62. Preparation and Characterization of Complex (η6-C5H5B OEt)RuCl(CCH2CH2CHCH3O)(PPh3) (6). A mixture of (η6-C5H5BOEt)RuCl(PPh3)2 (1a) (400 mg, 0.51 mmol) and racemic pent-4yn-2-ol (146 μL, 1.53 mmol) in toluene (30 mL) was stirred at 85 °C for about 24 h to give an orange suspension. The volume of the solution was reduced to approximately 1 mL under vacuum, and subsequent addition of n-hexane (10 mL) to the residue produced a yellow precipitate. The yellow solid was washed with n-hexane (2 × 10 mL) and diethyl ether (2 × 5 mL) and then dried under vacuum, which was identified to be a mixture of isomers 6a and 6b. Yield: 215 mg, 70%. Major isomer 6a: 31P{1H} NMR (202.5 MHz, CDCl3): δ 46.1 (s, RuPPh3). 1H NMR (850.1 MHz, CD2Cl2): δ 7.50−7.15 (m, 15H, PPh3, mixed with those of 6b), 6.12 (m, 1H), 5.56 (br, 1H), 5.03 (m, 1H), 4.68 (m, 1H, mixed with that of 6b), 4.49 (m, 1H), 3.68 (m, 4H), 3.13 (m, 1H), 2.12 (m, 1H), 1.90 (m, 1H), 1.19 (m, 3H mixed with that of 6a), 0.82 (m, 3H). 13C{1H} NMR (213.8 MHz, CD2Cl2): δ 317.5 (d, 2J(PC) = 18.4 Hz, RuC), 135.4−127.9 (m, PPh3), 120.6 (s, BCHCH), 104.5 (s, BCHCH), 93.3 (s, RuCOCH2), 78.0 (s, BCHCHCH), 72.5 (br, BCH), 60.5 (s, BOCH 2 ), 59.5 (s, RuCOCH 2 CH 2 ), 56.5 (br, BCH), 29.5 (s, RuCCH 2 ), 19.1 (RuCOCHCH3), 17.2 (s, BOCH2CH3). Minor isomer 6b: 31P{1H} NMR (202.5 MHz, CDCl3): 46.4 (s, RuPPh3). 1H NMR (850.1 MHz, CD2Cl2): δ 7.50−7.15 (m, 15H, PPh3, mixed with those of 6a), 6.09 (m, 1H), 5.48 (br, 1H), 4.68 (m, 1H, mixed with that of 6a), 3.92 (m, 1H), 3.88 (m, 3H), 3.73 (m, 1H), 3.66 (m, 1H), 3.59 (m, 1H), 2.08 (m, 1H), 1.84 (m, 1H), 1.53 (m, 1H), 1.50 (m, 3H), 1.19 (m, 3H mixed with that of 6a) . 13C{1H} NMR (213.8 MHz, CD2Cl2): δ 317.6 (d, 2J(PC) = 18.1 Hz, RuC), 135.4−127.9 (m, PPh3), 120.2 (s, BCHCH), 105.1 (s, BCHCH), 93.9 (s, RuCOCH2), 77.7 (s, BCHCHCH), 72.2 (br, BCH), 60.3 (s, BOCH 2 ), 60.2 (s, RuCOCH 2 CH 2 ), 57.5 (br, BCH), 29.0 (s, RuCCH 2 ), 20.4 (RuCOCHCH3), 17.1 (s, BOCH2CH3). 11B{1H} NMR (218.3 MHz,

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ASSOCIATED CONTENT

S Supporting Information *

X-ray crystallographic data for 1a, 1b, 2, 3, 4, and 6a (CIF), experimental procedures, and characterization data for new compounds. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/ acs.organomet.5b00319.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the National Basic Research Program of China (973 Program 2012CB821600), the National Natural Science Foundation of China (21072161), and Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT).

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REFERENCES

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Half-Sandwich B-Oxy Boratabenzene Ruthenium Complexes

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