Article pubs.acs.org/Organometallics
Preparation of Osmium η3‑Allenylcarbene Complexes and Their Uses for the Syntheses of Osmabenzyne Complexes Ting Bin Wen, Ka-Ho Lee, Jiangxi Chen, Wai Yiu Hung, Wei Bai, Huacheng Li, Herman H. Y. Sung, Ian D. Williams, Zhenyang Lin,* and Guochen Jia* Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong S Supporting Information *
ABSTRACT: Treatment of OsCl2(PPh3)3 with HCCAr (Ar = Ph, ptolyl) produced the η3-allenylcarbene complexes OsCl2(CAr-η2-CH CCHAr)(PPh3)2. Reactions of the η3-allenylcarbene complexes with gold alkynyls Au(CCR)(PPh3) (R = Ph, p-tolyl, TMS, nBu, CH(OEt)2) or copper(I) alkynyls Cu(CCR) (R = Ph, TMS) in the presence of HNEt3Cl produced the osmabenzynes Os{CC(R)C(CH2Ar)CH CAr}Cl2(PPh3)2. Computational studies suggest that the osmabenzynes are formed through electrocyclization of osmium alkynyl-allenylcarbene intermediates followed by protonation with HNEt3Cl.
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INTRODUCTION There has been much interest in the chemistry of transitionmetal-containing metallaaromatics.1,2 Metallabenzenes, in particular, have attracted considerable attention.3 A number of metallabenzenes with various substituents have been isolated especially for those of platinum, 4 iridium, 5 osmium, 6 ruthenium,7 and rhenium.8 Metallabenzynes are another interesting class of metallaaromatics that are structurally closely related to metallabenzenes. In contrast to metallabenzenes, reported well-characterized metallabenzynes are still limited.9,10 Syntheses of new metallabenzynes with different metals and substituents on the metallacycle remain as one of the major objectives in the development of the chemistry of metallabenzynes. Several strategies have been previously reported for the construction of metallabenzyne rings. The first isolated metallabenzyne (Os{CC(SiMe3)CMeC(SiMe3)CH}Cl2(PPh3)2) was obtained from the reaction of OsCl2(PPh3)3 with the alkyne HCCSiMe3.11 However, extension of the chemistry to prepare osmabenzynes involving reactions of OsCl2(PPh3)3 with other alkynes such as tert-butylacetylene12 and HCCC(OH)Ph213 was unsuccessful. Xia and his coworkers have shown that the osmium hydride vinylidene complex OsHCl2{CCH(PPh3)}(PPh3)2 can react with HCCCH(OEt)2 to give the PPh3-substituted osmabenzyne [Os{CC(PPh3)CHCHCH}Cl2(PPh3)2]Cl via an isoosmabenzene intermediate.14,15 Obviously this route can only be extended to prepare metallabenzynes derived from reactions involving acetal-functionalized alkynes. Other methods to construct metallabenzyne rings include zinc reduction of osmium vinylcarbyne complexes OsCl3(CCRCHCR CRX)(PPh3)2,16 oxidation of the osmium vinylcarbyne complex [OsHCl2{CC(PPh3)CHCPh}(PPh3)2]BF4,17 and thermal isomerization of rhenium vinylcarbyne complexes Re( CCHCRCCH)HCl(PMe2Ph)3.18 These routes are limited by the availability of vinylcarbyne complexes. Therefore, it is © XXXX American Chemical Society
desirable to explore other routes to construct metallabenzyne rings. In this work, we report the syntheses of a series of osmabenzynes from the reactions of η3-allenylcarbene complexes OsCl2(CAr-η2-CHCCHAr)(PPh3)2 with gold(I)/Cu(I) alkynyls. In particular, we will describe the syntheses of two η3-allenylcarbene complexes OsCl2(CAr-η2-CH CCHAr)(PPh3)2 from the reactions of OsCl2(PPh3)3 with HCCAr, report the reactions of these η3-allenylcarbene osmium complexes with gold(I)/Cu(I) alkynyls to give osmabenzynes, and discuss the mechanisms for the formation of the η3-allenylcarbene and osmabenzyne complexes. A preliminary report on this work has been published previously.19
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RESULTS AND DISCUSSION Synthesis and Characterization of η3-Allenylcarbene Complexes OsCl2(CAr-η2-CHCCHAr)(PPh3)2 (Ar = Ph, p-Tolyl). As mentioned in our preliminary report, the η3allenylcarbene complex OsCl2(CPh-η2-CHCCHPh)(PPh3)2 (2) could be prepared from the reaction of OsCl2(PPh3)3 (1) with HCCPh (Scheme 1).19 Under similar reaction conditions, OsCl2(PPh3)3 (1) reacted with HCC-p-tolyl to give the analogous η3-allenylcarbene complex OsCl 2 {C(p-tolyl)-η 2 -CHCCH(p-tolyl)}(PPh3)2 (3), which can be isolated in 66% yield. The structure and the NMR data of the η3-allenylcarbene complex OsCl2(CPh-η2-CHCCHPh)(PPh3)2 (2) have been briefly described in our preliminary report.19 However, the special structural and spectroscopic features deserve more detailed comments. A view of the molecular geometry of 2 is Special Issue: Organometallics in Asia Received: February 6, 2016
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DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
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delocalization of π electrons over the metal-coordinated C3 unit. On the basis of the structural data, this complex can be described as an η3-allenylcarbene complex with contribution from resonance structures 2, 2A, and 2B (Scheme 1). Similar structural features have been reported for η3-vinylcarbene complexes.26−28 The solid-state structure is supported by the solution NMR spectroscopic data. In particular, the 1H NMR spectrum of 2 at room temperature (298 K) showed two broad singlets at 2.30 and 5.60 ppm (in CD2Cl2), which can be assigned to the coordinated CH proton (H3) and the exocyclic CHPh proton (H1), respectively. In the 13C{1H} spectrum (in CD2Cl2), the formally carbene carbon displayed a triplet at 249.8 ppm (J(PC) = 7.5 Hz), which is in a slightly higher field than the resonance reported for the carbene carbons in typical osmium-carbene complexes (265−325 ppm)21−23,29and osmacyclopropene complexes (e.g., [Os{C(Ph)−CH 2 }H(OOCCH3)(PiPr3)2]BF4 (263.2 ppm)),30 indicative of contributions from resonance structure 2B to its actual structure. The η2-allenyl chain was characterized by a upfield resonance at 36.1 ppm for the CH carbon (η2-CHCCHPh) and a triplet at 136.6 ppm (J(PC) = 6.6 Hz) for the quaternary carbon (η2-CHCCHPh), as well as a singlet at 125.1 ppm for the exocyclic carbon (η2-CHCCHPh). As can be seen from the crystal structure of 2 (Figure 1), the two PPh3 ligands are inequivalent due to the coordination of the allenyl group to Os. At room temperature, complex 2 exhibited two very broad 31P{1H} signals at −8.4 and −28.1 ppm (in CD2Cl2). When the temperature was lowered to 263 K, the 31P{1H} signals appeared as two sharp doublets centered at −7.6 and −31.0 ppm with a large J(PP) coupling constant of 329.1 Hz, consistent with a trans disposition of the two PPh3 ligands in the solid-state structure. At temperatures above 320 K, the 31P{1H} NMR spectrum (in CDCl3) showed a single peak at −17.4 ppm. The fluxional behavior can be explained in terms of a change in the orientations of the coordinated CH group of the allenyl ligand.20 The structure of the η3-allenylcarbene complex 3 can be readily assigned on the basis of the fact that its NMR spectroscopic data are similar to those of the η3-allenylcarbene complex 2. In particular, the 31P{1H} NMR spectrum (in CD2Cl2) at room temperature showed two broad doublets at −7.0 and −29.1 ppm with a coupling constant of 327.7 Hz. The presence of the η3-allenylcarbene ligand is indicated by the 1H and 13C NMR data. In the 1H NMR spectrum (in CD2Cl2), the proton signals of the coordinated olefinic CH proton and the exocyclic CH(p-tolyl) proton of the allenyl group were observed at 2.16 and 5.56 ppm, respectively. The corresponding 13C signals in the 13C{1H} NMR spectrum (in CD2Cl2) were observed at 34.7 and 124.6 ppm, respectively. The 13C signals of OsCH(p-tolyl) and OsC(p-tolyl)-η2-CHC CH(p-tolyl) were observed at 248.9 and 135.7 ppm, respectively. The formation of the η3-allenylcarbene complexes OsCl2( CAr-η2-CHCCHAr)(PPh3)2 from the reactions of HC CAr with OsCl2(PPh3)3 (1) is interesting for the following reasons. First of all, although η3-vinylcarbene complexes26−28 are very common, reported η3-allenylcarbene complexes are still rare.31−33 Second, although coupling reactions of vinylidene species with alkynes to give allenylcarbene or metallacyclobutene intermediates have been proposed as early as 1980 as some of the key steps in metal-catalyzed oligomerization and polymerization of alkynes,34 very few examples of such coupling
Scheme 1. Preparation of η3-Allenylcarbene Complexes
shown in Figure 1.20 The most interesting structural feature of 2 is that it contains a four-membered metallacycle. The
Figure 1. Molecular structure of OsCl2(CPh-η2-CHCCHPh)(PPh3)2 (2). Selected bond distances (Å) and angles (degree): Os(1)−C(4) 1.895(9), Os(1)−C(3) 2.166(11), Os(1)−C(2) 2.069(11), C(4)−C(3), 1.432(15), C(3)−C(2) 1.445(15), C(2)− C(1) 1.319(15); C(4)−Os(1)−C(3) 40.6(4), C(4)−Os(1)−C(2) 75.9(4), C(3)−Os(1)−C(2) 39.8(4), C(21)−C(4)−C(3) 126.6(9), C(21)−C(4)−Os(1) 152.4, C(4)−C(3)−C(2) 116.1(10), C(3)− C(2)−C(1), 140.0(11), Os(1)−C(2)−C(1) 145.7(9).
PhCCHCCHPh moiety is coordinated to the Os center through C(2), C(3), and C(4) in a bent fashion, with the H atom on the C(3) carbon being closer to one of the PPh3 ligands. The two phenyl rings are almost coplanar with the atoms Cl(1), Cl(2), Os(1), C(2), and C(3). The phenyl ring on the exocyclic carbon C(1) is trans to the Os(1) center. The Os−C(4) bond distance (1.895(9) Å) is characteristic of an osmium−carbon double bond and is almost identical with those found in osmium carbene complexes such as OsCl2( CHCH2Ph)(CO)(PiPr3)2 (1.887(9) Å),21a [Os(O2CCH3)( C(CH3)C(OH)MePh)(PiPr3)2]BF4 (1.879(6) Å),21b OsCl2( CHPh)(CO)(PiPr3)2 (1.89(2) Å),22 and [OsCl(CHPh)(CO)(H2O)(PiPr3)2]BF4 (1.915(7) Å).23 The bond distances of Os−C(2) (2.069(11) Å) and Os−C(3) (2.166(11) Å) as well as C(2)−C(3) (1.441(15) Å) are comparable to those reported for η 2 -coordinated allene osmium complexes.6g,m,o,24,25 The C−C bond distances within the metallacycle (C(2)− C(3) = 1.445(15) Å, C(3)−C(4) = 1.432(15) Å) are significantly longer than a typical CC double bond (∼1.35 Å) but slightly shorter than the expected value for a single bond between two sp2 carbons (1.48 Å). The rather similar bond distances found for C(2)−C(3) and C(3)−C(4) indicate the B
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Organometallics reactions have been documented. The η1-allenylcarbene complexes Cp(CO)(NO)WC(NEt2)C(R)CHCMe3 (R = Me, Et) were isolated from the reactions of Cp(CO)(NO)WCCHCMe3 with the electron-rich alkynes RC CNEt 2 . 35 The metallacyclobutene complexes RuCl{C(COOMe)CHC[CH(C6H4Me)]}{P(C6H4Me)3}2(NO)36 and Cp*2Ti{C(R)C(R)CCH2}37 were isolated from the reactions of alkynes with RuCl{CCH(C6H4Me)]}{P(C6H4Me)3}2(NO) and Cp*2TiCCH2, respectively. η3Allenylcarbene complexes [CpRu(C(R′)-η 2-CHC CHR′)(PR3)]PF6 (R′ = ferrocenyl, R = Ph, Cy; R′ = ruthenocenyl, R = Ph), [CpOs{CPh-η2-CHCCHPh}(PiPr3)]BF4, and CpReBr2{C(SCH2Ph)-C(CH2Ph)C(SCH2Ph)C(SCH2Ph)2} were isolated from the reactions of [RuCp(PR3)(CH3CN)2]PF6 with ferrocenyl/ruthenocenyl acetylenes,31 the reaction of the dihydride dihydrogen complex [CpOsH2(η2-H2)(PiPr3)]BF4 with phenylacetylene,32 and the reaction of the η2-alkyne complex CpReBr2(η2-PhCH2SC CSCH2Ph) with PhCH2SCCSCH2Ph,33 respectively. Mechanism for the Formation of the η3-Allenylcarbene Complexes 2 and 3. To understand the reaction mechanism, we have monitored the reaction of OsCl2(PPh3)3 (1) with HCCPh by NMR. The 31P{1H} spectrum of the reaction mixture of OsCl2(PPh3)3 and HCCPh in C6D6, at the initial stage (5 min), showed a broad peak at −2.8 ppm for the starting material OsCl2(PPh3)3 (major) and a singlet at −6.0 ppm for the liberated PPh3, a singlet peak at 2.2 ppm for the vinylidene complex Os(CCHPh)Cl2(PPh3)2 (4),38 and four doublets at δ − 3.1, −4.8, −17.5, and −19.9 ppm. The 1 H NMR spectrum showed a triplet at 3.08 ppm for the vinylidene proton of 4 along with another triplet at 1.97 ppm (J(PH) = 3.1 Hz) with an intensity ratio of 3:1. Further study shows that the doublet 31P{1H} signals at δ − 3.1, −4.8, −17.5, and −19.9 ppm and the triplet 1H signal at 1.97 ppm are due to the triply chloro bridged dinuclear monovinylidene complex (PPh 3 ) 2 ClOs(μ-Cl) 3 Os(C CHPh)(PPh3)2 (5), which can be prepared by treatment of 4 with OsCl2(PPh3)3 (Scheme 2). Complex 5 represents a rare
Figure 2. Molecular structure of (PPh3)2ClOs(μ-Cl)3Os(C CHPh)(PPh3)2 (5). Selected bond distances (Å) and angles (deg): Os(1)−C(1) 1.800(18), C(1)−C(2) 1.24(2), C(2)−C(3) 1.46(2); Os(1)−C(1)−C(2) 178.7(14), C(1)−C(2)−C(3) 132.1(18).
can react with HCCPh to give the η3-allenylcarbene complex 2 and that treatment of isolated 5 with HCCPh produced initially a mixture of 4 and 2, and eventually 4 disappeared completely to give 2. On the basis of the observations described above, a plausible mechanism for the formation of the η3-allenylcarbene complexes is proposed in Scheme 2, with the formation of 2 as an illustration. The reaction of OsCl2(PPh3)3 (1) with HC CPh can initially lead to the formation of the vinylidene complexes 4 and 5, which could be detected at an early stage of the reaction when the reaction was monitored by NMR in C6D6. As it has been shown experimentally that the complex 5 can react with HCCPh to produce initially 4 and eventually 2, we believe that 4 is the real intermediate responsible for the formation of 2. The vinylidene complex 4 could bind another molecule of HCCPh to give the π-alkyne vinylidene intermediate Os(CCHPh)(η 2 -HCCPh)Cl 2 (PPh 3 ) 2 (4yne), which undergoes cycloaddition to produce complex 2. Similar [2 + 2] cycloaddition reactions involving an MC bond of carbene complexes have been observed for reactions of alkynes RCCR with Ru(CHPh)Cl2(H2IMes)(PCy3) (H2IMes =1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) to give η 3 -vinylcarbene complexes Ru(CR-η 2 -CRCHPh)Cl2(H2IMes)26 and the reaction of phenylacetylene with [Tp′(CO)2W{CHO(p-C6H4OMe)}]BF4 (Tp′ = hydridotris(3,5-dimethylpyrazolyl)borate) to give the η3-vinylcarbene complex [Tp′(CO)2W{CPh-η2-CHCHO(pC6H4OMe)}]BF4.27 [2 + 2] cycloaddition reactions of vinylidene complexes with alkynes have also been suggested as the key steps in the formation of η3-allenylcarbene complexes [CpRu(C(R′)-η2-CHCCHR′)(PR3)]PF6 (R′ = ferrocenyl, R = Ph, Cy; R′ = ruthenocenyl, R = Ph),31 [CpOs{ CPh-η2-CHCCHPh}(PiPr3)]BF4,32 and CpReBr2{C(SCH2Ph)C(CH2Ph)C(SCH2Ph)C(SCH2Ph)2}32 from reactions of alkynes with the respective complexes as mentioned above. The proposed mechanism is supported by computational studies. Figure 3 shows two calculated energy profiles for the formation of the model η3-allenylcarbene complex Os{ CC(Ph)C(CH2Ph)CHCPh}Cl2(PMe3)2 (2′, a model complex for 2) from the reaction of HCCPh with the model vinylidene complex Os(CCHPh)Cl2(PMe3)2 (4′, a model complex for 4), one involving initial direct addition of
Scheme 2. Isolation of Complex 5 and Proposed Mechanism for the Formation of Complex 2
example of a chloro-bridged dinuclear osmium vinylidene complex.39 Its structure has been established by a single-crystal X-ray structure analysis (Figure 2) and is supported by its NMR data. An in situ NMR experiment indicates that the η3allenylcarbene complex 2 was formed in 30 min, as evidenced by the 1H NMR spectrum, which displayed two broad singlets at 6.02 and 2.87 ppm (in C6D6) for the two allenyl protons. The 31P signals of OsCl2(PPh3)3, 4, and 5 decreased gradually on further reaction. It can also be demonstrated that isolated 4 C
DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
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have no experimental evidence for the formation of these species. Scheme 3. Possible Isomers of 2
Our computational studies suggest that the preferential formation of 2 rather than other isomeric products is of kinetic and thermodynamic origins. Figure 4 shows the energy profiles
Figure 3. Calculated energy profiles for the formation of the η3allenylcarbene complex 2′ from the vinylidene 4′ via an associative mechanism (a) and a dissociative mechanism (b). The relative Gibbs free energies and electronic energies (in parentheses) at 298 K are given in kcal/mol.
alkyne to 4′ (associative mechanism, Figure 3a) and the other involving initial dissociation of PMe3 from 4′ (dissociative mechanism, Figure 3b). As shown in Figure 3a, in the associative mechanism, the complex 4′ reacts with PhCCH to give the complex Os(CCHPh)(η 2 -HCCPh)Cl2(PMe3)2 (4yne′) endothermically with a barrier of 14.6 kcal/mol. The subsequent insertion of HCCPh into the OsC bond to give the η3-allenylcarbene complex 2′ is energetically favored by 19.0 kcal/mol with a barrier of 10.2 kcal/mol. Figure 3b shows the calculated energy profile for the reaction of 4′ with HCCPh to give 2′ involving the metal fragment Os(CCHPh)Cl2(PMe3) (4(-P)′) (dissociative mechanism). It is clear that the overall barrier for the formation of 2′ (37.8 kcal/mol) via the path shown in Figure 3b (37.8 kcal/ mol) is significantly higher than the overall barrier via the path shown in Figure 3a (14.6 kcal/mol), suggesting that the dissociative mechanism is kinetically less favorable than the associative mechanism. In contrast, it is generally accepted that metathesis reactions initiated by ruthenium complexes Ru( CR2)Cl2(L)2 proceed through a dissociation mechanism involving the 14e metal fragment Ru(CR2)Cl2(L).40 In our present case, an associative mechanism is favored, because osmium−ligand bonds are generally stronger than the corresponding ruthenium−ligand bonds. Indeed, dissociation of PMe3 from 4′ to give the five-coordinate complex OsCl2(PMe3) (4(-P)′) is energetically unfavored by 28.4 kcal/mol. The lower barrier via the associative mechanism is consistent with our experimental observations that η3allenylcarbene complexes can be formed at room temperature. In principle, reaction of OsCl2(PPh3)3 (1) with HCCPh could also produce other isomers such as η3-allenylcarbene complexes 2(I), 2(II), and 2(III) (Scheme 3). However, we
Figure 4. Calculated energy profiles for the formation of η3allenylcarbene complexes 2′, 2(I)′ (a), 2(II)′ and 2(III)′ (b) from vinylidene 4′ via an associative mechanism and the transformation of 2(II)′ to 2′ (c). The relative Gibbs free energies and electronic energies (in parentheses) at 298 K are given in kcal/mol. D
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Organometallics calculated for the formation of isomeric η3-allenyl complexes from the reaction of HCCPh with the model complex Os( CCHPh)Cl2(PMe3)2 (4′). As shown in Figure 4a, the formation of isomer 2(I)′ (a model complex for 2(I)) is both kinetically and thermodynamically less favorable than the formation of isomer 2′ (a model complex for 2). The energy profile shown in Figure 4b suggests that the formation of isomer 2(II)′ (a model complex for 2(II)) has a kinetic barrier similar to that for the formation of 2′ (Figure 4a). However, this isomer can transform to the thermodynamically more stable isomer 2′ via the five-coordinate intermediate 2(IV)′, as shown in Figure 4c. As shown in Figure 4b, the formation of the isomer 2(III)′ (a model complex for 2(III)) is less favorable both kinetically and thermodynamically than the formation of isomer 2(II)′. Reactions of OsCl2(CAr-η2-CHCCHAr)(PPh3)2 with Gold Alkynyls. The reactions of Au(CCPh)(PPh3) with the η3-allenylcarbene complexes 2 and 3 in the presence of HNEt3Cl at room temperature for ca. 3 h produced the osmabenzyne complexes 6a,b, respectively, which can be isolated as air-stable green solids (Scheme 4). Other aryl-
In addition to the successful isolation of the osmabenzynes described above, we have also carried out reactions of η3allenylcarbene complexes 2 and 3 with other gold(I) alkynyls such as Au(CCCO2Et)(PPh3), Au(CCtBu)(PPh3), and Au(CCH)(PPh3) in the presence of HNEt3Cl. Unfortunately, these reactions produced a mixture of phosphoruscontaining species, from which it is difficult to isolate pure products. Reactions of OsCl2(CAr-η2-CHCCHAr)(PPh3)2 with Copper Alkynyls. We are also interested in knowing if the relatively cheaper copper alkynyls instead of gold alkynyls could be used for the preparation of osmabenzynes. To test this possibility, we first studied the reactions of Cu(CCPh) with complexes 2 and 3 in the presence of HNEt3Cl. We were pleased to find that the reactions produced the corresponding osmabenzynes 6a,b, which can be isolated in 51.9% and 60% yields, respectively (Scheme 5). Similarly, reactions of Cu(C CSiMe3) with complexes 2 and 3 in the presence of HNEt3Cl produced the analogous osmabenzynes 9a,b, respectively. Scheme 5. Reactions of 2 and 3 with Cu(I) Acetylides
Scheme 4. Reactions of 2 and 3 with Au(I) Acetylides
Characterization of the Newly Synthesized Osmabenzynes. The osmabenzyne complexes Os{CCRC(CH2Ar)CHCAr}Cl2(PPh3)2 have been characterized by NMR spectroscopy and elemental analysis. Their 31P{1H} NMR spectra showed a singlet in the region of −5 to −10 ppm. The 1 H NMR spectra displayed a characteristic singlet signal for the CH proton of the metallacycle at 6.5−7.1 ppm. The 13C{1H} NMR spectra displayed an OsC signal at ca. 294−300 ppm and a signal for the other metal-bound carbon (OsC) at 209− 221 ppm. The 13C signals for the remaining carbons of the metallacycle were located at ca. 168−179, 114−125, and 133− 136 ppm, which correspond to C(CH2Ar), CH, and C(R), respectively. The structures of 6a,b, 7a,b, and 8a have been confirmed by X-ray diffraction studies. As a representative, the X-ray structure of Os{CC(p-tolyl)C(CH2−p-tolyl)CHC(p-tolyl))}Cl2(PPh3)2 (7b) is shown in Figure 5 (see the Supporting Information for other structures). For comparison, selected structural parameters associated with the metallacycles of these complexes are given in Tables S2 and S3 together with those of the “symmetrically” substituted osmabenzynes Os{CC(SiMe3)CC(CH3)C(SiMe3)CH}Cl2(PPh3)2 (11)11a and Os{CCHCC(CH3)CHCH}Cl2(PPh3)2 (12)41 in the Supporting Information. All of the complexes contain an essentially planar sixmembered metallacycle with the sum of internal angles in the six-membered ring being close to the ideal value of 720° required for a planar hexagon (see Table S2 in the Supporting Information). Subtle structural differences are noted for
substituted osmabenzynes could be similarly prepared from these η3-allenylcarbene complexes. For example, the analogous osmabenzyne complexes 7 could also be obtained from the reactions of Au(CC-p-tolyl)(PPh3) with 2 and 3 in the presence of HNEt3Cl. With this methodology, osmabenzynes having alkyl, TMS, and acetal substituents can also be prepared. For example, the n-butyl-substituted osmabenzynes 8 were obtained by treatment of 2 and 3 with Au{CC(CH2)3CH3}(PPh3) and HNEt3Cl (Scheme 4). The SiMe3-substituted osmabenzynes 9 can be similarly prepared from the reactions of 2 and 3 with Au(CCSiMe3)(PPh3) and HNEt3Cl. The acetal-substituted osmabenzyne 10b could also be isolated from the reaction of 3 with Au({CCH(OEt)2}PPh3) in the presence of HNEt3Cl. E
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carbon by HNEt3Cl followed by coordination of a chloride anion would give the osmabenzyne 16. The key step of the proposed mechanism is the electrocyclization of 14 to give 15. The process is reasonable, as electrocyclization of (Z)-hexa-1,3,5-triene to give 1,3-cyclohexadiene is a well-known example of a six-electron electrocyclization reaction allowed by the Woodward−Hoffmann rules.44 A similar electrocyclization process has been proposed for isomerization of the osmium alkynyl vinylcarbene complexes Os{C(CH 2 Ph)CHCHPh}(CCPh)Cl(PiPr3)245 and Os(CHCHCHR){CC(PPh3)}Cl(PPh3)2 (R = Ph, Et, vinyl, OEt)15a to give respectively the isometallabenzene complexes Os{C(CH2Ph)CHCH(Ph)C(Ph)CC}(CCPh)Cl(PiPr3)2 and Os{CHCHCH(R)C(PPh3)CC}(CCPh)Cl2(PPh3)2. To assess the feasibility of the proposed mechanism, computational studies were also carried out. Figure 6 shows
Figure 5. Molecular structure for Os{CC(p-tolyl)C(CH2(ptolyl))CHC(p-tolyl)}Cl2(PPh3)2 (7b).
complexes 6, 7, and 8a (with an aryl group at the C5 carbon) and complexes 11 and 12 (with no substituent at the C5 carbon). For example, the Os−C5 bonds of 6, 7, and 8a (2.052(12)−2.075(3) Å) are longer than those of 11 (1.939(5) Å) and 12 (2.008(7) Å). Concomitantly, the Os−C1 bond lengths of complexes 6, 7, and 8a (1.726(10)−1.766(5) Å) are shorter than those of 11 (1.815(4) Å) and 12 (1.805(7) Å). For complexes 6, 7, and 8a, the C2−C3 bonds are usually shorter than the C3−C4 bonds, while the two bonds have comparable distances for 11 and 12. The Os−Cl−C2 angles of complexes 6, 7, and 8a (153.4(6)−154.9(3)°) are appreciably larger than those of 11 (148.7(3)°) and 12 (148.3(6)°). The ring angles at C5 in 6, 7, and 8a (123.8(3)−125.8(8)°) are appreciably smaller than those in 11 (138.6(5)°) and 12 (132.1(5)°), while the angles at C4 in 6, 7, and 8a (126.4(10)− 128.9(4)°) are much more obtuse than those in 11 (117.7(4)°) and 12 (123.5(6)°). Mechanism for the Formation of Metallabenzynes. A plausible mechanism for the formation of osmabenzynes from the reactions of η3-allenylcarbene complexes OsCl2(CAr-η2CHCCHAr)(PPh3)2 with gold(I)/Cu(I) alkynyls is shown in Scheme 6, using the reaction of 2 with M(CCR)
Figure 6. Calculated energy profiles for the formation of the osmabenzyne 21 from η3-allenylcarbene complexes 17 and 18. The relative Gibbs free energies and electronic energies (in parentheses) at 298 K are given in kcal/mol.
Scheme 6. Proposed Mechanism for the Formation of Osmabenzynes
the calculated energy profile for the formation of osmabenzyne 21 (a model complex for 16) starting from the model alkynylallenylcarbene complexes 17 (a model complex for 13) and 18 (a model complex for 13a). Complexes 17 and 18 have very similar energies, with 17 being slightly more stable. The rearrangement of complexes 17 and 18 to the 16e species 19 is energetically favored by 4.1 and 5.2 kcal/mol with barriers of 2.6 and 14.6 kcal/mol, respectively. The electrocyclization of complex 19 occurs easily with a very small barrier of 6.8 kcal/ mol to give the more stable metallacycle 20. The protonation of 20 by HNMe3Cl to give 21 is thermodynamically favored by 9.5 kcal/mol. The computational results confirm that the proposed mechanism shown in Scheme 6 is feasible. It is interesting to note that the activation energy for the electrocyclization of complex 19 to give 20 (6.8 kcal/mol) is significantly smaller than that for electrocyclization of (Z)-hexa1,3,5-triene to give 1,3-cyclohexadiene (29.9 kcal/mol).46 Summary. We have developed an efficient synthetic route for the preparation of osmabenzynes from the reactions of osmium η3-allenylcarbene complexes OsCl2(CAr-η2-CH CCHAr)(PPh3)2 with Au(I) or Cu(I) alkynyls. This method allows us to synthesize osmabenzynes with various substituents under mild reaction conditions. Computational studies suggest
(M = Cu, Au(PPh3)) as an illustration. It is known that Cu(I)42 and Au(I)43 alkynyls can undergo transmetalation reactions with transition-metal halide complexes to give transition-metal alkynyl complexes. The reaction of an alkynyl species M(C CR) with the η3-allenylcarbene complex 2 may lead to the formation of the osmium alkynyl complex 13 or 13a with the elimination of MCl. The complex 13 or 13a may evolve to the five-coordinate complex 14, which undergoes electrocyclization to give the metallacycle 15. Finally, protonation at the CHPh F
DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
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Organometallics
for an additional 8 h to give a brown solution, which was concentrated to ca. 2 mL. Addition of ether (20 mL) to the residue produced a light brown solid and a brownish green solution. The solid was collected by filtration, washed with ether (2 × 15 mL), and dried under vacuum overnight. Yield: 0.33 g, 58%. 31P{1H} NMR (121.5 MHz, C6D6): ABA′B′ pattern, δ −3.2 (d), −5.0 (d) (J(PAPB) = 12.1 Hz); −17.6 (d), −20.0 (d) (J(PA′PB′) = 17.6 Hz). 1H NMR (300.13 MHz, C6D6): δ 1.97 (t, J(PH) = 3.2 Hz, 1 H, OsCCH), 6.95−8.02 (m, 65 H, C6H5, PPh3). 13C{1H} NMR (100.4 MHz, CD2Cl2): δ 313.9 (dd, J(PC) = 13.4, 10.4 Hz, OsC), 138.7−125.2 (m, C6H5, PPh3), 113.4 (s, OsCCH). Anal. Calcd for C80H66Cl4P4Os2: C, 57.42; H, 3.98. Found: C, 57.10; H, 4.25. Os{CCPhC(CH2Ph)CHCPh}Cl2(PPh3)2 (6a). A mixture of Os(CPh-η2-CHCCHPh)Cl2(PPh3)2 (503 mg, 0.51 mmol) and Cu(CCPh) (110 mg, 0.67 mmol) in CH2Cl2 (50 mL) was stirred at room temperature for 15 min to give a brown solution. HNEt3Cl (551 mg, 4.00 mmol) was added, and the mixture was stirred at room temperature for 24 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (5 mL). The solution was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove the impurities and then eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 288 mg, 51.9%. The complex 6a could also be made using Au(CCPh)(PPh3) instead of Cu(CCPh) (see the Supporting Information of our preliminary report19). 31P{1H} NMR (121.5 MHz, CDCl3): δ −9.9 (s). 1H NMR (300.13 MHz, CDCl3): δ 3.73 (s, 2 H, −CH2Ph), 5.64 (d, J(HH) = 7.2 Hz, 2 H, o-C6H5), 6.32 (d, J(HH) = 7.0 Hz, 2 H, o-C6H5), 6.76 (t, J(HH) = 7.2 Hz, 2 H, mC6H5), 6.82 (s, 1 H, OsCPhCH−), 6.88 (t, J(HH) = 7.2 Hz, 1 H, pC6H5), 6.91 (dd, J(HH) = 3.9 Hz, J(HH) = 3.6 Hz, 2 H, m-C6H5), 7.13−7.32 (m, 24 H, PPh3, C6H5), 7.49−7.56 (m, 12 H, PPh3). 13 C{1H} NMR (100.40 MHz, CDCl3): δ 294.8 (t, J(PC) = 12.0 Hz, OsC), 213.9 (t, J(PC) = 5.5 Hz, OsCPh), 167.9 (s, C-CH2Ph), 156.8 (s, ipso-C6H5), 138.7 (s, ipso-C6H5), 135.2 (t, J(PC) = 4.6 Hz, oPPh3), 133.3 (s, OsCPhCH−), 131.5 (t, J(PC) = 26.8 Hz, ipsoPPh3), 130.8 (s, o-C6H5), 130.1 (s, p-PPh3), 128.9 (s, m-C6H5), 128.6 (s, m-C6H5), 127.5 (t, J(PC) = 5.5 Hz, m-PPh3), 127.4 (s, p-C6H5), 127.3 (s, ipso-C6H5), 127.2 (s, o-C6H5), 126.5 (s, o-C6H5), 125.3 (s, OsCCPh), 125.1 (s, p-C6H5), 124.7 (s, m-C6H5), 40.3 (s, CH2Ph), (one of the para carbons of C6H5 could not unambiguously be assigned, which is probably obscured by other aromatic resonances). Anal. Calcd for C60H48Cl2OsP2: C, 65.99; H, 4.43. Found: C, 66.21; H, 4.62. FAB-MS (NBA, m/z): calcd for C60H48Cl2OsP2 [M − Cl]+, 1057.25; found, 1057.5. Os{CCPhC(CH2-p-tolyl)CHC(p-tolyl)}Cl2(PPh3)2 (6b). Method A, from Au(CCPh)(PPh3). A mixture of Os(C(p-tolyl)η2-CHCCH(p-tolyl))Cl2(PPh3)2 (0.50 g, 0.50 mmol) and Au(CCPh)(PPh3) (0.40 g, 0.74 mmol) in CH2Cl2 (20 mL) was stirred at room temperature for 15 min to give a brown solution, HNEt3Cl (0.80 g, 5.81 mmol) was added, and the mixture was stirred at room temperature for 3 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (5 mL). The extractant was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove Au(PPh3)Cl and other impurities and then eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 0.16 g, 29%. Method B, from Cu(CCPh). A mixture of Os{C(p-tolyl)-η2CHCCH(p-tolyl)}Cl2(PPh3)2 (0.260 g, 0.26 mmol) and Cu(C CPh) (0.050 g, 0.30 mmol) in CH2Cl2 (20 mL) was stirred at room temperature for 15 min to give a brown solution, HNEt3Cl (0.283 g, 2.06 mmol) was added, and the mixture was stirred at room temperature for 18 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (5 mL). The extractant was filtered through Celite to remove the insoluble
that the osmabenzynes are formed through electrocyclization of osmium alkynyl-allenylcarbene intermediates followed by protonation by HNEt3Cl.
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EXPERIMENTAL SECTION
All manipulations were carried out under a nitrogen atmosphere using standard Schlenk techniques unless otherwise stated. Solvents were distilled under nitrogen from sodium benzophenone (benzene, ether, hexane), or calcium hydride (CH2Cl2). The starting materials OsCl2(PPh3)3 (1),47 Os(CCHPh)Cl2(PPh3)2 (4),38 Au(C CR)(PPh3),48 and Cu(CCR) (R = Ph, SiMe3)49 were prepared by following the procedures described in the literature. All other reagents were used as purchased from Aldrich Chemical Co. Microanalyses were performed by M-H-W Laboratories (Phoenix, AZ). 1H, 13C{1H}, and 31P{1H} spectra were collected on a Bruker ARX-400 spectrometer (400 MHz), a JEOL EX-400 spectrometer (400 MHz), or a Bruker ARX-300 spectrometer (300 MHz). 1H and 13 C NMR shifts are relative to TMS, and 31P chemical shifts are relative to 85% H3PO4. Os(CPh-η2-CHCCHPh)Cl2(PPh3)2 (2). The complex was obtained from the reaction of OsCl2(PPh3)3 with PhCCH following a procedure described in the Supporting Information of our preliminary report.19 31P{1H} NMR (121.5 MHz, CD2Cl2): 298 K, AB pattern δ −8.4 (br s), −28.1 (br s); 210 K: δ −8.3 (d), −32.3 (d), J(PAPB) = 329.1 Hz. 1H NMR (300.13 MHz, CD2Cl2): 298 K, δ 2.30 (s (br), W1/2 = 6.5 Hz, 1 H, OsCPh(η2-CHC)), 5.60 (s (br), W1/2 = 6.8 Hz, 1 H, CCCHPh), 6.63−7.84 (m, 37 H, C6H5, PPh3), 9.36 (br, W1/2 ≈ 106.0 Hz, 1 H, C6H5); 210 K, δ 2.27 (t, J(PH) = 5.6 Hz, 1 H, OsCPh(η2−CHC), 5.78 (s (br), W1/2 = 7.0 Hz, 1 H, CCCHPh), 6.61−7.85 (m, 37 H, C6H5, PPh3), 9.29 (d, J(HH) = 7.7 Hz, 1 H, C6H5). 13C{1H} NMR (100.4 MHz, CD2Cl2, 298 K): δ 249.8 (t, J(PC) = 7.5 Hz, Os = CPh), 145.4 (s, C6H5), 136.7 (s, C6H5), 136.6 (t, J(PC) = 6.6 Hz, η2-CHCCHPh), 135.4− 126.7 (m, other aromatic carbons), 125.1 (s, CCCHPh), 36.1 (s, OsCPh(η2-CHC)). Anal. Calcd for C52H42Cl2P2Os: C, 63.09; H, 4.28. Found: C, 63.00; H, 4.24. FAB-MS (NBA, m/z): calcd for C52H42Cl2P2Os [M+], 990.18; found, 990.3. Os{C(p-tolyl)-η2-CHCCH(p-tolyl)}Cl2(PPh3)2 (3). To a benzene (12 mL) solution of OsCl2(PPh3)3 (0.80 g, 0.76 mmol) was added 4-ethynyltoluene (0.96 mL, 7.6 mmol). The reaction mixture was stirred at room temperature for 10 h to give a large amount of green precipitates. The green solid was collected by filtration, washed with benzene (2 mL) and ether (2 × 10 mL), and dried under vacuum overnight. Yield: 0.51 g, 66%. 31P{1H} NMR (121.5 MHz, CD2Cl2): 298 K, AB pattern δ −7.0 (br s), −29.1 (br s), J(PAPB) ≈ 327.7 Hz; 243 K, δ −7.9 (d), −31.0 (d), J(PAPB) = 329.9 Hz. 1H NMR (300.13 MHz, CD2Cl2): 298 K, δ 2.10 (s, 3 H, C6H4CH3), 2.16 (s (br), W1/2 = 5.6 Hz, 1 H, OsC(p-tolyl)(η2-CHC), 2.40 (s, 3 H, C6H4−CH3), 5.56 (s (br), W1/2 = 5.8 Hz, 1 H, CC CH(p-tolyl)), 6.83−7.56 (m, 37 H, C6H4, PPh3), 9.29 (br, W1/2 ≈ 67.0 Hz, 1 H, C6H4); 243 K, δ 2.10 (s, 3 H, C6H4-CH3), 2.14 (ddd, J(PH) = 7.6, 5.6 Hz, J(HH) = 2.0 Hz, 1 H, OsC(p-tolyl)(η2-CHC), 2.37 (s, 3 H, C6H4−CH3), 5.68 (s (br), W1/2 = 6.0 Hz, 1 H, CCCH(ptolyl)), 6.75−7.73 (m, 37 H, C6H4, PPh3), 9.29 (d, J(HH) = 8.0 Hz, 1 H, C6H4). 13C{1H} NMR (100.4 MHz, CD2Cl2, 298 K): δ 248.9 (t, J(PC) = 7.4 Hz, OsC), 145.5 (s, C6H4), 143.3 (s, C6H4), 136.2 (s, C6H4), 135.7 (t, J(PC) = 7.2 Hz, η2-CHCCH(p-tolyl)), 135.6− 126.6 (m, other aromatic carbons), 124.6 (s, η2-CHCCH(ptolyl)), 34.7 (s, η2-CHCCH(p-tolyl)), 23.2, 20.9 (s × 2, C6H4CH3). Anal. Calcd for C54H46Cl2P2Os: C, 63.71; H, 4.55. Found: C, 63.67; H, 4.70. (PPh3)2ClOs(μ-Cl)3Os(CCHPh)(PPh3)2 (5). A mixture of Os(CCHPh)Cl2(PPh3)2 (0.30 g, 0.34 mmol) and OsCl2(PPh3)3 (0.53 g, 0.50 mmol) in CH2Cl2 (40 mL) was stirred at room temperature for 18 h. The solvent was removed under vacuum, and the brownish green residue was washed with hexane (40 mL) and filtered to remove free PPh3. The brownish green solid was dried under vacuum, and additional OsCl2(PPh3)3 (0.18 g, 0.17 mmol) was added. The resulting mixture was further stirred in 40 mL of CH2Cl2 G
DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
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Organometallics HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove the impurities and then eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 0.171 g, 60%. 31 1 P{ H} NMR (121.5 MHz, CD2Cl2): δ −8.6 (s). 1H NMR (300.13 MHz, CD2Cl2): δ 2.21 (s, 3 H, OsC(p-tolyl)), 2.30 (s, 3 H, CH2(ptolyl)), 3.68 (s, 2 H, −CH2(p-tolyl)), 5.66 (d, J(HH) = 7.5 Hz, 2 H, mCH of OsC(p-tolyl)), 6.35 (d, J(HH) = 7.8 Hz, 2 H, m-CH of −CH2(p-tolyl)), 6.60 (d, J(HH) = 8.1 Hz, 2 H, o-CH of OsC(ptolyl)), 6.71 (s, 1 H, OsC(p-tolyl)CH), 6.80 (d, J(HH) = 7.8 Hz, 2 H, o-CH of OsCC(Ph)), 7.05 (d, J(HH) = 7.5 Hz, 2 H, o-CH of −CH2(p-tolyl)), 7.19 (t, J(HH) = 7.5 Hz, 12 H, m-PPh3), 7.29 (t, J(HH) = 7.5 Hz, 2 H, m-CH of OsCC(Ph)), 7.37 (t, J(HH) = 7.2 Hz, 6 H, p-PPh3), 7.47−7.53 (m, 12 H, PPh3), 7.57 (t, J(HH) = 8.4 Hz, 1 H, p-CH of OsCC(Ph)). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ 295.7 (t, J(PC) = 12.8 Hz, OsC), 214.5 (t, J(PC) = 5.4 Hz, OsC(p-tolyl)), 169.3 (s, C-CH2(p-tolyl)), 154.7 (s, ipso-OsC(ptolyl)), 136.6 (s, p-CH2(p-tolyl)), 136.2 (s, p-OsCC(Ph)), 133.8 (s, OsC(p-tolyl)CH), 135.6−125.8 (m, other aromatic carbons), 125.5 (s, OsCCPh), 40.2 (s, CH2(p-tolyl)), 21.1 (s, C6H4CH3), 21.0 (s, C6H4CH3). Anal. Calcd for C62Cl2H52P2Os· CH2Cl2: C, 62.79; H, 4.52. Found: C, 62.96; H, 4.20. Os{CC(p-tolyl)C(CH2Ph)CHCPh}Cl2(PPh3)2 (7a). The complex was obtained from the reaction of 2 with Au{CC(ptolyl)}(PPh3) in the presence of HNEt3Cl (see the Supporting Information of our preliminary report19). 31P{1H} NMR (121.5 MHz, CDCl3): δ −9.6 (s). 1H NMR (300.13 MHz, CDCl3): δ 2.53 (s, 3 H, OsCC6H4-CH3)), 3.83 (s, 2 H, CH2Ph), 5.76 (d, J(HH) = 6.6 Hz, 2 H, o-CH of OsCC(p-tolyl))), 6.34 (d, J(HH) = 6.3 Hz, 2 H, mCH of OsCC(p-tolyl)), 6.86 (s, OsCPhCH), 6.76−7.64 (m, other aromatic proton). 13C{1H} NMR (75.5 MHz, CDCl3): δ 295.0 (t, J(PC) = 12.8 Hz, OsC), 212.8 (t, J(PC) = 5.9 Hz, OsCPh), 168.1 (s, C-CH2Ph), 156.8 (s, ipso-C6H5), 138.8 (s, ipso-C6H5), 137.1 (s, OsCPhCH−), 125.2 (s, OsCC(p-tolyl)), 135.2−124.2 (m, other aromatic carbons), 40.2 (s, CH2Ph), 21.2 (s, CH3). Anal. Calcd for C61Cl2H50P2Os·0.5CH2Cl2: C, 64.31; H, 4.48. Found: C, 64.14; H, 4.54. Os{CC(p-tolyl)C(CH2(p-tolyl))CHC(p-tolyl)}Cl2(PPh3)2 (7b). A mixture of Os(C(p-tolyl)-η2-CHCCH(p-tolyl))Cl2(PPh3)2 (0.50 g, 0.50 mmol) and Au(CC(p-tolyl)) (0.34 g, 0.59 mmol) in CH2Cl2 (20 mL) was stirred at room temperature for 15 min to give a brown solution. HNEt3Cl (0.80 g, 5.81 mmol) was added, and the mixture was stirred at room temperature for 3 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (5 mL). The solution was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove Au(PPh3)Cl and other impurities and then eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 0.21 g, 37%. 31P {1H} NMR (121.5 MHz, CDCl3): δ −9.3 (s). 1H NMR (300.13 MHz, CDCl3): δ 2.18 (s, 3 H, OsC(C6H4CH3)), 2.31 (s, 3 H, OsCC(C6H4-CH3)), 2.40 (s, 3 H, −CH2(C6H4-CH3)), 3.64 (s, 2 H, -CH2-tolyl), 5.61 (d, J(HH) = 8.1 Hz, 2 H, m-CH of OsC(p-tolyl)), 6.20 (d, J(HH) = 7.9 Hz, 2 H, mCH of −CH2(p-tolyl)), 6.56 (d, J(HH) = 8.1 Hz, 2 H, o-CH of OsC(ptolyl)), 6.77 (s, 1 H, OsC(tolyl)CH-), 6.78 (d, J(HH) = 7.9 Hz, 2 H, o-CH of OsCC(p-tolyl)), 6.96 (d, J(HH) = 7.9 Hz, 2 H, o-CH of −CH2(p-tolyl)), 7.02 (d, J(HH) = 7.9 Hz, 2 H, m-CH of Os CC(p-tolyl)), 7.14 (t, J(HH) = 7.6 Hz, 12 H, m-PPh3), 7.30 (t, J(HH) = 7.3 Hz, 6 H, p-PPh3), 7.49−7.55 (m, 12 H, PPh3). 13C{1H} NMR (100.40 MHz, CDCl3): δ 294.1 (t, J(PC) = 12.7 Hz, OsC), 213.2 (t, J(PC) = 6.3 Hz, OsC(tolyl)), 168.0 (s, C-CH2−tolyl), 153.7 (s, ipso- OsC(p-tolyl)), 136.7 (s, p-CH2(p-tolyl)), 135.7 (s, pOsCC(p-tolyl)), 135.6 (s, ipso-CH2(p-tolyl)), 134.9 (t, J(PC) = 5.1 Hz, o-PPh3), 134.3 (s, p-OsC(p-tolyl)), 133.3 (s, OsC(p-tolyl) CH−), 131.3 (t, J(PC) = 26.6 Hz, ipso-PPh3), 130.4 (s, m-CH2(p-
tolyl)), 129.8 (s, p-PPh3), 129.0 (s, m-OsCC(p-tolyl)), 128.7 (s, oCH2(p-tolyl)), 128.6 (s, o-OsCC(p-tolyl)), 127.3 (s, m-OsC(ptolyl)), 127.2 (t, J(PC) = 5.1 Hz, m-PPh3), 125.2 (s, o-OsC(ptolyl)), 124.6 (s, OsCC(tolyl)), 124.1 (s, ipso-CH2(p-tolyl)), 40.0 (s, −CH2-tolyl), 21.4 (s, −CH2C6H4-CH3), 21.2 (s, Os CC(C6H4-CH3) and OsC(C6H4-CH3)) (the ipso carbon of Os CC(p-tolyl) could not unambiguously be assigned, which is probably merged with other aromatic resonances). Anal. Calcd for C63H54Cl2OsP2: C 66.72, H 4.80. Found: C 66.37, H 5.11. Os{CC((CH2)3CH3)C(CH2Ph)CHCPh}Cl2(PPh3)2 (8a). The complex was obtained from the reaction of 2 with Au(C C(CH2)3CH3)(PPh3) in the presence of HNEt3Cl (see the Supporting Information of our preliminary report19). 31P{1H} NMR (121.5 MHz, CDCl3): δ −10.7 (s). 1H NMR (300.13 MHz, CDCl3): δ 0.80−0.90 (m, 5 H, CH2CH3), 1.11−1.18 (m, 2 H, CH2CH3), 1.18 (quintet, J(HH) = 7.5 Hz, 2 H, CH2CH2CH3), 2.10 (t, J(HH) = 8.4 Hz, 2 H, CH2CH2CH2CH3), 3.82 (s, 2 H, CH2Ph), 5.49 (d, J(HH) = 7.5 Hz, 2 H, o-C6H5), 6.71 (s, 1 H, OsCPhCH−), 6.72 (t, J(HH) = 7.8 Hz, 2 H, m-C6H5), 6.86 (t, J(HH) = 7.2 Hz, 1 H, p-C6H5), 7.03 (d, J(HH) = 7.2 Hz, 2 H, o-C6H5), 7.24−7.40 (m, 16 H, PPh3, C6H5), 7.55−7.61 (m, 17 H, PPh3, C6H5). 13C{1H} NMR (75.5 MHz, CDCl3): δ 298.8 (t, J(PC) = 8.6 Hz, OsC), 209.4 (t, J(PC) = 6.4 Hz, OsCPh), 169.1 (s, C-CH2Ph), 156.6 (s, ipso-C6H5), 138.3 (s, ipso-C6H5), 133.7 (s, OsCPhCH−), 135.2−124.5 (m, other aromatic carbons), 123.0 (s, OsCC((CH2)3CH3)), 40.1 (s, CH2Ph), 32.8 (s, CH2), 23.3 (s, CH2), 21.6 (s, CH2), 13.6 (s, CH3). Anal. Calcd for C58Cl2H52P2Os: C, 64.98; H, 4.89. Found: C, 65.04; H, 4.68. Os{CC((CH 2 ) 3 CH 3 )C(CH 2 (p-tolyl))CHC(p-tolyl)}Cl2(PPh3)2 (8b). A mixture of Os{C(p-tolyl)-η2-CHCCH(ptolyl)}Cl2(PPh3)2 (0.50 g, 0.50 mmol) and Au{CC(CH2)3CH3}(PPh3) (0.40 g, 0.74 mmol) in CH2Cl2 (20 mL) was stirred at room temperature for 15 min to give a brown solution, HNEt3Cl (0.80 g, 5.81 mmol) was added, and the mixture was stirred at room temperature for 2 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (5 mL). The extractant was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove Au(PPh3)Cl and other impurities and then further eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 0.16 g, 29%. 31 1 P{ H} NMR (121.5 MHz, CD2Cl2): δ −9.9 (s). 1H NMR (300.13 MHz, CD2Cl2): δ 0.67−0.76 (m, 5 H, CH2CH3), 1.12 (quintet, J(HH) = 7.5 Hz, 2 H, CH2CH2CH3), 2.06 (t, J(HH) = 8.1 Hz, 2 H, CH2CH2CH2CH3), 2.15 (s, 3 H, OsCC6H4-CH3)), 2.33 (s, 3 H, C−CH2(C6H4-CH3)), 3.73 (s, 2 H, CH2(C6H4-CH3)), 5.39 (d, J(HH) = 8.1 Hz, 2 H, o-CH of OsCC(C6H4-CH3))), 6.49 (d, J(HH) = 7.8 Hz, 2 H, o-CH of OsCC(C6H4-CH3))), 6.54 (s, 1 H, OsC(C6H4−CH3)CH−), 6.72 (t, J(HH) = 7.8 Hz, 2 H, m-C6H5), 6.87−7.52 (m, 34 H, other aromatic protons). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ 299.8 (t, J(PC) = 11.4 Hz, OsC), 210.2 (t, J(PC) = 5.9 Hz, OsC(C6H4-CH3)), 170.7 (s, C-CH2(C6H4-CH3)), 154.6 (s, ipso-(C6H4-CH3)), 135.6 (s, ipso-(C6H4-CH3)), 133.8 (s, OsC(C6H4-CH3)CH−), 134.7−125.7 (m, other aromatic carbons), 123.1 (s, OsCC((CH2)3CH3)), 40.0 (s, CH2(C6H4-CH3)), 33.2 (s, CH2), 23.7 (s, CH2), 21.9 (s, CH2), 21.1 (s, C6H4-CH3), 20.9 (s, C6H4-CH3), 13.8 (s, CH3). Anal. Calcd for C60Cl2H58P2Os·1.5CH2Cl2: C, 60.08; H, 5.00. Found: C, 60.19; H, 4.85. Os{CC(SiMe3)C(CH2Ph)CHCPh}Cl2(PPh3)2 (9a). A mixture of Os(CPh-η2-CHCCHPh)Cl2(PPh3)2 (1.031 g, 1.04 mmol) and Cu(CCSiMe3) (220 mg, 1.37 mmol) in CH2Cl2 (60 mL) was stirred at room temperature for 15 min to give a brown solution, HNEt3Cl (1.113 g, 8.08 mmol) was added, and the mixture was stirred at room temperature for 24 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (15 mL). The extractant was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove the H
DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
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Organometallics impurities and then eluted with dichloromethane/ether (5:/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 0.402 g, 35.5%. The complex 9a could also be made using Au(CCSiMe3)(PPh3) instead of Cu(CCSiMe3) (see the Supporting Information of our preliminary report19). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ −9.1 (s). 1H NMR (300.13 MHz, CD2Cl2): δ 0.18 (s, 9 H, Si(CH3)3), 3.85 (s, 2 H, −CH2Ph), 5.62 (d, J(HH) = 7.8 Hz, 2 H, o-C6H5), 6.48 (s, 1 H, OsCPhCH), 6.67 (t, J(HH) = 7.5−7.8 Hz, 2 H, m-C6H5), 6.82 (t, J(HH) = 6.9−7.5 Hz, 1 H, p-C6H5), 7.04 (d, J(HH) = 7.2 Hz, 2 H, o-C6H5), 7.23−7.40 (m, 21 H, PPh3, C6H5), 7.47−7.51 (m, 12 H, PPh3, C6H5). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ 300.6 (t, J(PC) = 11.9 Hz, OsC), 221.2 (t, J(PC) = 12.9 Hz, OsCPh), 179.3 (s, CCH2Ph), 156.9 (s, ipso-C6H5), 139.0 (s, ipso-C6H5), 136.1 (s, OsCPhCH−), 135.7−124.9 (m, other aromatic carbons), 114.2 (s, OsCC(SiMe3)), 44.6 (s, −CH2Ph), 1.6 (s, Si(CH3)3). Anal. Calcd for C57Cl2H52P2OsSi: C, 62.91; H, 4.82. Found: C, 62.68; H, 5.02. Os{CC(SiMe3)C(CH2(p-tolyl))CHC(p-tolyl)}Cl2(PPh3)2 (9b). Method A, from Au(CCSiMe3)(PPh3). A mixture of Os{ C(p-tolyl)-η2-CHCCH(p-tolyl)}Cl2(PPh3)2 (0.22 g, 0.22 mmol) and Au(CCSiMe3)(PPh3) (0.18 g, 0.33 mmol) in CH2Cl2 (15 mL) was stirred at room temperature for 15 min to give a brown solution, HNEt3Cl (0.24 g, 1.73 mmol) was added, and the mixture was stirred at room temperature for 2 days. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (5 mL). The extractant was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene, dichloromethane, and dichloromethane/ether (20/1) subsequently to remove Au(PPh3)Cl and other impurities and then eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 0.13 g, 53%. Method B, from Cu(CCSiMe3). A mixture of Os{C(p-tolyl)-η2CHCCH(p-tolyl)}Cl2(PPh3)2 (0.510 g, 0.50 mmol) and Cu(C CSiMe3) (0.091 g, 0.57 mmol) in CH2Cl2 (25 mL) was stirred at room temperature for 15 min to give a brown solution, HNEt3Cl (0.552 g, 4.01 mmol) was added, and the mixture was stirred at room temperature for 2 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (15 mL). The extractant was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 1 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove the impurities and then eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a green solid, which was dried under vacuum. Yield: 0.224 g, 40.6%. 31P{1H} NMR (121.5 MHz, C6D6): δ −10.0 (s). 1H NMR (300.13 MHz, C6D6): δ 0.17 (s, 9 H, Si(CH3)3), 2.06 (s, 3 H, OsCC6H4CH3)), 2.13 (s, 3 H, CH2(C6H4CH3)), 3.77 (s, 2 H, CH2(C6H4CH3)), 6.01 (d, J(HH) = 7.8 Hz, 2 H, m-CH of OsCC(C6H4CH3))), 6.64 (d, J(HH) = 7.5 Hz, 2 H, m-CH of OsCC(C6H4CH3))), 6.85−6.96 (m, 23 H, OsC(p-tolyl)CH−, aromatic protons), 7.88−7.96 (m, 12 H, other aromatic protons). Anal. Calcd for C59Cl2H56P2OsSi.0.5CH2Cl2: C, 61.68; H, 4.96. Found: C, 61.52; H, 5.09. Os{CCH(O(CH 2 CH 3 ) 2 )C(CH 2 (p-tolyl))CHC(p-tolyl)}Cl2(PPh3)2 (10b). A mixture of Os(C(p-tolyl)-η2-CHCCH(ptolyl))Cl 2 (PPh 3 ) 2 (0.50 g, 0.50 mmol) and Au(CCC(O(CH2CH3)2H)(PPh3) (0.30 g, 0.41 mmol) in CH2Cl2 (20 mL) was stirred at room temperature for 20 min to give a brown solution, HNEt3Cl (0.50 g, 3.63 mmol) was added, and the mixture was stirred at room temperature for 3 h. The solvent was completely removed under vacuum, and the resulting solid was extracted with benzene (5 mL). The extractant was filtered through Celite to remove the insoluble HNEt3Cl. The filtrate was concentrated to ca. 3 mL and was loaded onto a silica gel column. The column was flashed with benzene and dichloromethane subsequently to remove Au(PPh3)Cl and other impurities and then eluted with dichloromethane/ether (5/1) to give a green solution. The solvent was removed under vacuum to give a
green solid, which was dried under vacuum. Yield: 0.20 g, 35%. 31 1 P{ H} NMR (121.5 MHz, C6D6): δ −5.1 (s). 1H NMR (300.13 MHz, C6D6): δ 1.00 (t, J(HH) = 6.9 Hz, 6 H, 2 OCH2CH3), 2.07 (s, 3 H, C6H4-CH3), 2.14 (s, 3 H, C6H4-CH3), 3.01 (quintet, J(HH) = 6.9 Hz, 2 H, OCH2CH3), 3.18 (quintet, J(HH) = 6.9 Hz, 2 H, OCH 2 CH 3 ), 4.02 (s, 2 H, -CH 2 (p-tolyl)), 5.33 (s, 1 H, −CH(OCH2CH3)2), 6.22 (d, J(HH) = 7.5 Hz, 2 H, o-CH of −CH2(p-tolyl)), 6.74 (d, J(HH) = 8.1 Hz, 2 H, o-CH of −CH2(ptolyl)), 6.80−7.89 (m, 34 H, PPh3, C6H4-CH3), 7.11 (s, 1 H, OsC(tolyl)CH). The 13C{1H} NMR spectrum was not collected because the compound partially decomposed in the solution during collection of the 13C{1H} NMR spectrum. X-ray Crystallography. The procedure for crystallographic analyses of 2, 6a, 7a, and 8a can be found in the Supporting Information of our preliminary report.19 Single crystals of 5, 6b, and 7b suitable for X-ray diffraction were grown from CH2Cl2 solutions layered with hexane. Intensity data were collected on a Bruker SMART CCD Area Detector at 293 K for 5 and 7b and on an Oxford Gemini S Ultra Area Detector at 173 K for 6b. All of the data were corrected for absorption effects using the multiscan technique. All structures were solved by direct methods, expanded by difference Fourier syntheses, and refined by full -matrix least squares on F2 using the SHELXTL v. 6.1050 or OLEX251 program package. All non-H atoms were refined anisotropically, and hydrogen atoms were placed in ideal positions and refined as riding atoms unless specified. The p-tolyl group of the benzyl substituent in 6b was disordered over two sites, which were refined isotropically with half occupancy. One of the Cl atoms of the CH2Cl2 solvent molecule in 6b was disordered over three sites, which were also refined with isotropic thermal parameters with partial occupancy. Further crystallographic details for 2·C7H8, 5, 6a·CH2Cl2, 6b·2CH2Cl2, 7a·CH2Cl2, 7b, and 8a·2CH2Cl2 are summarized in Table S1 in the Supporting Information. Computational Details. All structures were optimized without any constraint at the B3LYP-D3 level of density functional theory (DFT).52 Frequency calculations were also performed to identify all the stationary points as minima (zero imaginary frequency) or transition states (one imaginary frequency) and to provide free energies at 298.15 K. The effective core potentials (ECPs) of Lanl2dz were used to describe Os, Cl, and P atoms,53 with polarization functions for Os (ζ(f) = 0.886), Cl (ζ(d) = 0.640), and P (ζ(d) = 0.387) being added.54 The standard 6-31G(d) basis set was used for all other atoms (C, N, and H atoms). To take solvation effects into consideration, we preformed singlepoint energy calculations at the same level of theory augmented with the SMD solvation model to obtain the optimized structures.55 Following the experimental work, dichloromethane (DCM) was employed as the solvent in the single-point energy calculations. To reduce the overestimation of the entropy contribution in the gas-phase results, corrections of −2.6 (or +2.6) kcal/mol in free energies were made for 2:1 (or 1:2) transformations.56 In this paper, the solvationand entropy-corrected free energies were used in all of our discussions. All calculations were performed with the Gaussian 09 software package.57
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00102. Crystallographic data of complexes 2, 5, 6a,b, 7a,b, and 8a and NMR spectra (PDF) Crystallographic data of complexes 2, 5, 6a,b, 7a,bm and 8a (CIF) Cartesian coordinates of all calculated structures (XYZ) I
DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
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Organometallics
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AUTHOR INFORMATION
Corresponding Authors
*E-mail for Z.L.:
[email protected]. *E-mail for G.J.:
[email protected]. Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by the Hong Kong Research Grants Council (Project Nos. 602611, 601812, 602113, CUHK7/ CRF/12G-2).
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DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
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DOI: 10.1021/acs.organomet.6b00102 Organometallics XXXX, XXX, XXX−XXX
