Oxidative addition of halogen across an Os-Os or Os-Sb bond: Formation of five-membered osmium-antimony carbonyl rings

Journal of Organometallic Chemistry 811 (2016) 66e73

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Oxidative addition of halogen across an Os-Os or Os-Sb bond: Formation of five-membered osmium-antimony carbonyl rings Ying-Zhou Li, Rakesh Ganguly, Weng Kee Leong* Division of Chemistry & Biological Chemistry, Nanyang Technological University, 21 Nanyang Link, 637371, Singapore

a r t i c l e i n f o

a b s t r a c t

Article history: Received 4 March 2016 Received in revised form 21 March 2016 Accepted 22 March 2016 Available online 24 March 2016

Halogenation of the cluster Os3(CO)10(m-SbPh2)2, 2, with PhICl2 or I2 affords the five-membered metallacyclic rings Os3(Cl)2(CO)10(m-SbPh2)2, 3d and Os3(I)2(CO)10(m-SbPh2)2, 3d-I, respectively, via oxidative addition across an OseOs bond. The reaction of 2 with SbPh2Cl or SbPh2H gives the 3,5-fused rings Os3(X)(CO)9(m-SbPh2)3, (X ¼ Cl, 4a; H, 4b), respectively. Halogenation of 4 with PhICl2 gives the fivemembered metallacyclic rings Os3(Cl)(X)(CO)9(SbPh2Cl)(m-SbPh2)2 (X ¼ Cl, 5a; H, 5b) via oxidative addition across an OseSb bond. The analogous reaction with I2 also results in oxidative addition across an OseSb bond, but this is followed by displacement of SbPh2I to afford a five-membered metallacycle containing a m-I ligand, viz., Os3(m-I)(X)(CO)9(m-SbPh2)2 (X ¼ Cl, 7a, H, 7b). © 2016 Elsevier B.V. All rights reserved.

Keywords: Halogen Oxidative addition Five-membered rings Osmium Antimony

1. Introduction Metallacycles are of interest for applications which are based on their host-guest chemistry. While there are numerous studies on self-assembled metallacycles employing a multitude of multidentate ligands to link the metals [1], studies on metallacycles with direct metal-metal bonds are much less common, probably due to the lack of efficient synthetic methods [2]. Such metal-metal bonded metallacycles, especially heterometallic forms comprising a transition metal and a main-group metal/metalloid, may show interesting behaviour. One recent example is that of a sixmembered hetero-metallacycle composed of Re and Sb, which exhibits interesting host-guest interaction between the ring metals and Pd metal [3]. General synthetic routes to such metal-metal bonded heterometallacycles should therefore be of interest. An interesting route to the construction of larger metallacycles is through ring-opening reactions with smaller fused ring systems; we have earlier demonstrated this strategy through the cleavage of OseOs bonds via nucleophilic addition [4]. An attractive alternative means to the cleavage of a metal-metal bond is via an oxidative addition reaction. We have previously reported that Os3(CO)10(NCCH3)2, 1,

* Corresponding author. E-mail address: [email protected] (W.K. Leong). http://dx.doi.org/10.1016/j.jorganchem.2016.03.025 0022-328X/© 2016 Elsevier B.V. All rights reserved.

undergoes SbeCl oxidative addition with SbPh2Cl to afford three isomeric five-membered metallacycles Os3(Cl)2(CO)10(m-SbPh2)2, 3a-c, in relatively low yields (Scheme 1) [2h]. A retrosynthetic analysis suggests that they should be available through a reaction of the previously reported cluster Os3(CO)10(m-SbPh2)2, 2, with Cl2 [5]. More recently, we have also reported that reaction of the ruthenium analogue Ru3(CO)10(NCCH3)2, 1-Ru, with Sb2Ph4 proceeded via SbeSb oxidative addition across an RueRu bond to form the ruthenium-antimony fused ring compound Ru3(CO)10(mSbPh2)2, 2-Ru. This in turn reacted with SbPh2Cl via SbeCl oxidative addition to form the 5-membered metallacycle Ru3(Cl)(CO)9(mSbPh2)3, 4a-Ru [6]. Clusters such as 2 and 4 are in themselves promising precursors to larger ruthenium-antimony metallacycles through the cleavage of the RueRu bond in the triangular fragment, but we were thwarted by the relatively low thermal stability of these clusters. In this report, we have prepared the osmium analogues Os3(CO)10(m-SbPh2)2, 2, and Os3(X)(CO)9(m-SbPh2)3, (X ¼ Cl, 4a; H, 4b), and investigated their reactivity towards halogens. 2. Results and discussion Cluster 2 was previously prepared from the reaction of Os3(CO)10(m-H)(m-SbPh2) with SbPh2Cl [5]. We have found that it can also be obtained in an improved yield (74%) via the reaction of 1 with Sb2Ph4, in analogy to that for its ruthenium analogue 2-Ru. As

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Scheme 1. Oxidative addition reaction of 1 with SbPh2Cl.

expected, the reaction of 2 with PhICl2 (the synthetic equivalent for Cl2) at room temperature proceeds readily to give two isomeric five-membered metallacycles, the previously reported 3b, and a new stereoisomer 3d (Scheme 2). The analogous reaction with I2 affords only the iodo analogue of the latter, viz., 3d-I. The structures of both 3d and 3d-I have been determined by single-crystal X-ray crystallographic analyses, and ORTEP plots showing their structures are given in Fig. 1. Cluster 3d is the fourth, new stereoisomer for the metallacycles 3. The other two previously reported isomers, viz., 3a and 3c, are not observed in this reaction. Cluster 3d was not detected (by 1H NMR monitoring) in the original reaction given in Scheme 1, indicating that its formation here follows a different pathway. The crystal structure of 3d exhibits a 1:1 disorder corresponding to a two-fold rotation through the unique Os (bonded to two Sb atoms), which implies that the Cl ligand on that Os atom could be in either of the two nonequivalent equatorial positions (Fig. S1). The 1 H NMR spectrum shows only two sets of chemically nonequivalent phenyl rings (Fig. S5), which suggests that only one of the two possible isomers implied from the disorder is present. Fortunately, the crystal structure of 3d-I is well-behaved and shows unambiguously that the two I ligands adopt the stereochemistry depicted in Scheme 2. It is therefore assumed that 3d has the same stereochemistry. All the five-membered rings, viz., 3d and 3d-I, as well as the previously reported isomers 3a-c, adopt an envelope-like conformation; the mean deviation from the Os3Sb2 best plane for the envelope is in the range 0.08e0.18 Å, and the dihedral angle between that plane and the flap plane is ~40 (Table S2 and Fig. S3). The weaker trans influence of I compared to Cl is reflected in the shorter Os2eSb1 bond length in 3d-I (2.6547(8) Å compared to

2.6807(9) Å in 3d). The stereochemistry of 3d implies that the reaction may be viewed as an oxidative addition of Cl2 across the SbPh2-bridged OseOs bond in 2, and is reminiscent of the electrophilic addition of halogens across alkenes, although the exact reaction mechanism is still unclear. A solution of 3d converts to 3b, slowly at room temperature and more rapidly at elevated temperatures. This conversion has been observed by 1H NMR spectroscopy (Fig. S7), and it is consistent with a computational study which shows that 3b lies 38.9 kJ/mol below 3d (Fig. S30). In analogy with the ruthenium system [6], the oxidative addition reaction of 2 with SbPh2X gives the fused ring cluster Os3(X)(CO)9(m-SbPh2)3 (X ¼ Cl, 4a; or H, 4b) (Scheme 3). Both 4a and 4b are stable in solution; there is no observable decomposition at ambient conditions over several days. They have also been fully characterized, including by an X-ray crystallographic analysis for 4a. That 4b has an analogous structure is supported by the pattern for the CO stretching vibrations in its IR spectrum, which is similar to that of 4a (Fig. S29); the terminal hydride exhibits a 1H resonance at d 7.26 ppm (Fig. S12). The ORTEP plot depicting the molecular structure of 4a, together with selected bond parameters, is given in Fig. 2. Like its ruthenium analogue, the metal core of 4a also comprises a five-membered Os3Sb2 ring and an envelope flap-like Os2Sb unit. The fivemembered ring is slightly puckered, with a mean deviation of ~0.24 Å from the best plane, and the dihedral angle between the Os3Sb2 ring and the Os2Sb flap is ~10 . The OseSb bond lengths for the triangular Os2Sb unit are shorter than those in the fivemembered Os3Sb2 ring, consistent with centrally-directed, threecentre-two-electron bonds in the former; this is believed to lead to

Scheme 2. Reaction of 2 with halogens leading to the cleavage of an OseOs bond.

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Fig. 1. ORTEP diagrams of the molecular structures of 3d (left) and 3d-I (right). Thermal ellipsoids are drawn at the 50% probability level. Organic hydrogen atoms have been omitted for clarity.

Scheme 3. The reactions of 2 with SbPh2Cl or SbPh2H.

Fig. 2. ORTEP plot of the molecular structure of 4a. Thermal ellipsoids are drawn at the 50% probability level. Organic hydrogen atoms have been omitted for clarity. Selected interatomic bond distances (Å) and bond angles ( ): Os2eOs3 ¼ 3.0029(8), Os3eSb6 ¼ 2.5962(13), Sb6eOs2 ¼ 2.5887(11), Os3eSb4 ¼ 2.6546(11), Sb4eOs1 ¼ 2.6962(9), Os1eSb5 ¼ 2.7107(10), Sb5eOs2 ¼ 2.6628(10), Os1eCl1 ¼ 2.423(3), Os2eSb6eOs3 ¼ 70.78(3), Sb6eOs3eOs2 ¼ 54.49(3), Os3eSb4eOs1 ¼ 121.57(4), Os1eSb5eOs2 ¼ 122.26(3).

shortening of the metal-metal bonds present in trinuclear carbonyl clusters such as Os3(CO)12 and Os2Cr(CO)11[(PMe)3]2 [7]. Our attempts at cleaving the remaining OseOs bond in 4a with halogens to form a six-membered ring were unsuccessful. The reaction with PhICl2 gives an almost quantitative yield of a product which has been characterized as Os3(Cl)2(CO)9(SbPh2Cl)(m-SbPh2)2, 5a. This hydrolyses during TLC separation to afford a derivative which has been tentatively identified as Os3(Cl)2(CO)9(SbPh2OH)(mSbPh2)2, 6a (Scheme 4). Cluster 4b reacts analogously to afford Os3(H)(Cl)(CO)9(SbPh2X)(m-SbPh2)2 (X ¼ Cl, 5b; or OH, 6b). Despite numerous attempts, we have not been able to obtain diffraction-quality crystals of these products except for 6b. Nevertheless, the purity of the initial products 5 from these reactions is attested to by their spectroscopic characteristics. The pattern of the CO stretches in the IR spectra of 5 and 6 are very similar, indicating structural similarity (Fig. S29). The 13C{1H} NMR spectra of both 5a and 5b show nine carbonyl resonances, consistent with the low symmetry (Figs. S14eS19). Their mass spectra show a cluster of peaks centred at 1722 and 1687, respectively, which correspond to an [M-Cl]þ fragment and consistent with their formulation as Cl2 adducts of 4 (Fig. S28). Likewise, the mass spectra of 6a and 6b show a cluster of peaks centered at 1703 and 1668, respectively, which correspond to an [M-Cl]þ fragment, and supporting the presence of an SbeOH group. The crystallographic analysis on 6b suggests that it has cocrystallized with a small amount (17%) of 6a. The presence of the latter is corroborated by the 1H NMR spectrum of the sample, which shows resonances ascribable to 6a (Figs. S16 and S19). The ORTEP diagram showing the molecular structure of 6b is given in Fig. 3.

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Scheme 4. Reactions of 4 with PhICl2.

The SbPh2OH and Cl ligands occupy equatorial positions. The presence of an SbeOH moiety supports our belief that 5 contains an SbeCl group which probably underwent hydrolysis during TLC separation on silica; a similar hydrolysis of an SbeBr bond during TLC separation has been observed previously [8]. This hydrolysis reaction may also account for the small amount of 6a which cocrystallised out; excess/residual PhICl2, or HCl resulting from the hydrolysis of 5b, would have converted the terminal hydride to a chloro ligand [9]. The cluster core of 6b adopts an envelope-like conformation; the Os1eSb4eOs3eSb5 plane has a mean deviation from planarity of ~0.040 Å, and the dihedral angle between that plane and the Os1eOs2eSb5 flap plane is ~43 . The reaction of 4 with I2 leads, on the other hand, to the iodobridged products Os3(X)(CO)9(m-I)(m-SbPh2)2 (X ¼ Cl, mer-7a; H, mer-7b). Presumably, the initial products of the reactions are the intermediates Os3(X)(I)(CO)9(SbPh2I)(m-SbPh2)2 (X ¼ Cl, B; H, B′), which then eliminates SbPh2I (Scheme 5).

The clusters mer-7 isomerise (more readily with mer-7b than with mer-7a, which requires heating) to their fac isomers fac-7. This conversion process has been followed by 1H NMR spectroscopy (Figs. S24 and S27), and may involve simultaneous turnstile rotations about the Os atoms bridged by the iodo ligand. A computational study shows that mer-7a and mer-7b lie 13 and 41 kJ/mol above fac-7a and fac-7b, respectively. The isomers in which the bridging iodide and Cl or H are on the same side of the metal ring plane have not been observed experimentally, consistent with the computational study which shows that they lie 31 and 5 kJ/mol, respectively, above the mer isomers. The structures of mer-7a, fac-7a and fac-7b have been characterized by X-ray crystallographic analyses. Two crystallographically distinct molecules with similar bond parameters are found for fac7b. The ORTEP diagrams showing the molecular structures for the two isomers of 7a are given in Fig. 4; selected bond parameters for all three clusters, with a common atomic labelling scheme, are collected in Table 1. The metal cores of all three structures adopt an envelope conformation, with the Sb1eOs3eSb2 unit forming the envelope flap. The bridging iodo ligand in mer-7a is in the same plane as the metal core, but is perpendicular to the metal core plane and on the side opposite to the chloro/hydrido ligand in fac-7. The OseSb bond lengths trans to the bridging iodo ligand in mer-7a (Os2eSb1 and Os1eSb2) are much shorter than those in fac-7a, indicating that the iodo ligand has a weak trans influence. The OseSb bond lengths in the envelope flap (Sb1eOs3eSb2) of fac-7b are also significantly shorter than those in fac-7a (2.7007(6) and 2.6941(7) Å vs 2.6537(5)-2.6688(5) Å, respectively) although the other OseSb bond lengths are similar. This may possibly be attributed to the reduced steric repulsion between the axial carbonyls on the Os1 and Os2 centres, and the hydrido ligand in fac-7b, compared to the chloro ligand in fac-7a. This also manifests itself in the significantly more planar metal core of fac-7b, with a mean deviation of <0.09 Å from the best plane (Fig. S4).

3. Conclusion

Fig. 3. ORTEP plots of the molecular structures of 6b. Thermal ellipsoids are drawn at the 50% probability level. Organic hydrogen atoms have been omitted for clarity. Selected bond distances (Å) and bond angles ( ): Os1eOs2 ¼ 2.9931(4), Os2eSb5 ¼ 2.6837(5), Sb5eOs3 ¼ 2.6818(5), Os3eSb4 ¼ 2.6680(5), Sb4eOs1 ¼ 2.6369(5), Os2eSb6 ¼ 2.6085(6), Sb6eO6 ¼ 1.943(5), Os1eCl1 ¼ 2.4893(19), Os2eSb6eO6 ¼ 123.29(17), Os1eOs2eSb5 ¼ 90.791(13), Os2eSb5eOs3 ¼ 118.819(18), Sb5eOs3eSb4 ¼ 86.680(16), Os3eSb4eOs1 ¼ 124.595(19), Sb4eOs1eOs2 ¼ 95.636(14).

In this work, we have described ring-opening to fivemembered osmium-antimony metallacycles via the oxidative addition of halogens to metal-metal bonds. In comparison to the oxidative addition of an SbeCl bond reported earlier, the method presented here offers greater stereospecificity and a much higher yield, under mild reaction conditions. The latter characteristic makes it possible to prepare thermally unstable metallacycles such as their ruthenium analogues. That attempted ring-opening to sixmembered rings led to oxidative addition across an OseSb bond instead of an OseOs bond is intriguing and deserves further investigation in the future.

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Scheme 5. Reaction of 4 with I2.

4. Experimental General Data. All manipulations were carried out under an argon atmosphere with standard Schlenk techniques. Reagent grade solvents were dried by the standard procedures and were freshly distilled prior to use. Ph2SbCl, Ph2SbH and PhICl2 were prepared as described in the literatures [10]. TLC separations were carried out on 20  20 cm2 plates coated with silica gel 60 F254 from Merck. NMR spectra were recorded on a 400 MHz NMR spectrometer at room temperature unless otherwise specified. All 1 H and 13C chemical shifts were referenced to the residual proton resonance, and the 13C resonance, of the deuterated solvent used. Mass spectra were recorded in ESI-ToF mode. Elemental analyses were carried out in-house. 4.1. Preparation of 2 Cluster 1 (50 mg, 54 mmol) was dissolved in dry DCM (10 ml). To this was added Sb2Ph4 (36 mg, 65 mmol). After 6 d of stirring at

room temperature, the solvent was removed in vacuo. The residue was separated by TLC with DCM/Hexane (1:1, v/v) as the eluent to give 2 as the major product. Rf ¼ 0.70. Yield ¼ 52 mg (74%). Its identity was determined by comparison of its IR and 1H NMR with the literature values [5]. 4.2. Reaction of 2 with PhICl2 Cluster 2 (20 mg, 14 mmol) was dissolved in DCM (10 ml) and PhICl2 (5.0 mg, 18 mmol) was then added. The resulting mixture was stirred at room temperature for 24 h, resulting in a nearly colorless solution. The solvent was removed and the residue separated by TLC, with DCM/hexane (1:1, v/v) as the eluent, to give two main bands. Band 1, light yellow, was identified as 3b. Rf ¼ 0.45. Yield ¼ 3 mg (14%). Band 2, light yellow, was identified as 3d. Rf ¼ 0.30. Yield ¼ 15 mg (71%). IR (CH2Cl2): n(CO) 2120w, 2106m, 2072w, 2059w, 2036vs, 2016w, 2003w, 1985w cm1. 1H NMR (C6D6): d 7.80

Fig. 4. ORTEP plots of the molecular structures of mer-7a (left) and fac-7a (right). Thermal ellipsoids are drawn at the 50% probability level. Organic hydrogen atoms have been omitted for clarity.

Y.-Z. Li et al. / Journal of Organometallic Chemistry 811 (2016) 66e73 Table 1 Common atom-labeling scheme and selected bond lengths (Å) and angles ( ) for clusters mer-7a, fac-7a and fac-7b.

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135.67, 135.57, 132.17, 130.50, 130.39, 129.63, 129.52, 129.50, 129.42, 128.82, 128.54, 128.21. Anal. Calcd for C45H30O9ClOs3Sb3: C 32.05, H 1.79. Found: C 32.17, H 1.64. ESI-MSþ (m/z): 1687 [MþH]þ. 4.5. Reaction of 2 with SbPh2H

Os1eOs2 Os2eSb1 Os3eSb1 Os3eSb2 Os1eSb2 Os2eSb1eOs3 Os1eSb2eOs3 Dihedral angle ( )a Mean deviation (Å)b a b

mer-7a

fac-7a

fac-7b Molecule 1

Molecule 2

2.9154(7) 2.6356(8) 2.7255(8) 2.7183(9) 2.6341(8) 123.67(3) 120.93(2) 26.2 e

2.8872(5) 2.7255(7) 2.7007(6) 2.6941(7) 2.7034(7) 122.39(2) 126.30(2) 26.9 e

2.9011(4) 2.7020(5) 2.6644(5) 2.6537(5) 2.7133(5) 126.364(19) 128.692(19) 6.7 0.057

2.8981(4) 2.7140(5) 2.6688(5) 2.6641(5) 2.7137(5) 125.922(18) 127.614(17) 6.1 0.083

Dihedral angle between the Os1eOs2eSb1eSb2 and the Sb1eOs3eSb2 planes. Mean deviation from Os1eOs2eSb1eOs3eSb2 plane.

(d, 4H, Ph), 7.31 (d, 4H, Ph), 6.95e7.09 (m, 12H, Ph). 13C{1H} NMR (CDCl3): d (CO) 185.70 (2C), 181.51 (2C), 177.48 (2C), 169.46 (1C), 168.73 (1C), 167.91 (1C), 167.09 (1C); d (Ph) 135.90, 134.59, 130.80, 130.03, 129.44, 128.64, 125.94, 125.73. Anal. Calcd for C34H20O10Cl2Os3Sb2: C 27.71, H 1.37. Found: C 27.58, H 1.51. ESIMSþ: 1493 [MþH2OþH]þ, 1369 [MþCH3CNe4COeCl]þ. 4.3. Reaction of 2 with I2 Cluster 2 (20 mg, 14 mmol) was dissolved in DCM (10 ml) and I2 (5.0 mg, 20 mmol) was then added. The resulting mixture was stirred at room temperature for 12 h, resulting in a nearly colorless solution. The solvent was removed and light yellow crystal of 3d-I was obtained after recrystallization in DCM and hexane. Yield ¼ 16 mg (68%). IR (CH2Cl2): n(CO) 2115w, 2100m, 2066w, 2056w, 2032vs, 2003w, 1985w cm1. 1H NMR (C6D6): d 7.75 (d, 4H, Ph), 7.32 (d, 4H, Ph), 6.96e7.10 (m, 12H, Ph). 13C{1H} NMR (CDCl3): d (CO) 182.87 (2C), 182.01 (2C), 175.25 (2C), 168.93 (1C), 168.37 (1C), 167.60 (1C), 166.38 (1C); d (Ph) 136.03, 134.57, 130.80, 130.05, 129.41, 128.46, 126.96, 126.93. Anal. Calcd for C34H20O10I2Os3Sb2: C 24.65, H 1.22. Found: C 24.71, H 1.04. ESI-MSþ: 1530 [M-I]þ. 4.4. Reaction of 2 with SbPh2Cl Cluster 2 (20 mg, 14 mmol) was dissolved in DCM (10 ml) and CH3CN (2 ml). TMNO (1.08 mg, 14 mmol) was dissolved in CH3CN (4 ml) and added dropwise over 5 min. The resulting mixture was stirred at room temperature for 20 min and then the solvent was removed in vacuo. Sb2Ph2Cl (10 mg, 32 mmol) was added, followed by dry THF (10 ml), to give an orange solution. The reaction mixture was stirred at 40  C for 96 h, the solvent was removed and the residue separated by TLC with DCM/hexane (1:1, v/v) as the eluent, to give one major band of 4a. Rf ¼ 0.65. Yield ¼ 19 mg (76%). IR (CH2Cl2): n(CO) 2095m, 2075w, 2039s, 2004s, 1973w cm1. 1H NMR (C6D6) d 8.04 (d, 4H, Ph), 7.76 (d, 4H, Ph), 7.51e7.58 (m, 4H, Ph), 6.88e7.13 (m, 18H, Ph). 13C{1H} NMR (CDCl3): d (CO) 183.72 (2C), 183.37 (2C), 180.46 (2C), 171.48 (1C), 171.35 (2C); d (Ph) 135.76,

Cluster 2 (20 mg, 14 mmol) was dissolved in DCM (10 ml) and CH3CN (2 ml). TMNO (1.1 mg, 14 mmol) was dissolved in CH3CN (4 ml) and added dropwise over 5 min. The resulting mixture was stirred at room temperature for 20 min and then the solvent was removed in vacuo. To the light yellow residue, SbPh2H/hexane solution (0.50 ml, ca. 50 mmol) was added followed by addition of dry DCM (10 ml), resulting in an orange solution. The reaction mixture was stirred at room temperature for 96 h, the solvent was removed and the residue separated by TLC with DCM/hexane (1:1, v/v) as the eluent, to give one major band of 4b. Rf ¼ 0.75. Yield ¼ 16 mg (68%). IR (CH2Cl2): n(CO) 2081m, 2066m, 2031s, 1995s, 1968m cm1. 1H NMR (C6D6): d 7.97 (d, 4H, Ph), 7.90 (d, 4H, Ph), 7.54 (dd, 2H, Ph), 7.47 (dd, 2H, Ph), 6.87e7.15 (m, 18H, Ph)?7.26 (s, 1H,OsH). 13C{1H} NMR (CDCl3): d (CO) 185.79 (2C), 184.69 (2C), 181.17 (2C), 179.60 (1C), 176.02 (2C); d (Ph) 135.40, 135.33, 135.20, 130.38, 130.33, 129.79, 129.57, 129.50, 129.46, 129.29, 129.23, 129.12, 128.68, 128.44. Anal. Calcd for C45H31O9Os3Sb3: C 32.72, H 1.89. Found: C 33.03, H 2.02. ESI-MSþ (m/z): 1652 [MþH]þ. 4.6. Reaction of 4a with PhICl2 Cluster 4a (20 mg, 12 mmol) was dissolved in DCM (10 ml) followed by addition of PhICl2 (6.5 mg, 24 mmol). The resulting light yellow solution was stirred at room temperature for 24 h, leading to a nearly colorless solution. The solvent was removed in vacuo and the residue (crude of 5a) was further dried in vacuo overnight to remove the excess PhICl2, which would decompose into benzene and Cl2 under vacuum. NMR spectra of the residue showed 5a was pure enough. Yield ¼ 23 mg (almost quantitatively). IR (CH2Cl2): n(CO) 2102m, 2085w, 2049s, 2012s, 1992w cm1. 1H NMR (C6D6) d 7.97e8.04 (m, 6H, Ph), 7.81e7.85 (t, 4H, Ph), 7.61 (d, 2H, Ph), 6.88e7.12 (m, 18H, Ph). 13C{1H} NMR (CDCl3): d (CO) 189.98 (1C), 188.81 (1C), 188.67 (1C), 186.86 (1C), 171.72 (1C), 170.38 (1C), 170.34 (1C), 169.28 (1C), 169.08 (1C); d (Ph) 137.83, 137.21, 136.16, 135.94, 135.86, 135.43, 134.44, 134.20, 130.97, 130.90, 130.37, 130.22, 130.07, 130.00, 129.96, 129.70, 129.67, 129.34, 129.23, 129.08, 128.98, 128.94, 128.53, 128.50. Anal. Calcd for C45H30O9Cl3Os3Sb3: C 30.76, H 1.72. Found: C 30.60, H 1.72. ESI-MSþ (m/z): 1722 [M-Cl]þ, 1694 [M-CO-Cl]þ, 1666 [M-2COeCl]þ. Compound 5a was dissolved in DCM and repurified by TLC, with pure DCM as the eluent, to give one main band affording 6a. Rf ¼ 0.55. Yield ¼ 12 mg (58%). IR (CH2Cl2): n(CO) 2100m, 2082w, 2046s, 2011s, 1987w cm1. 1H NMR (C6D6): d 8.00 (d, 2H, Ph), 7.84e7.90 (m, 8H, Ph), 7.62 (d, 2H, Ph), 6.93e7.11 (m, 18H, Ph), 1.57 (s, broad, 1H, SbOH). ESI-MSþ: 1722 [M-OH]þ, 1703 [M-Cl]þ. Analogues 5b and 6b were prepared according to the similar method to that for 5a and 6a, respectively. Cluster 5b: IR (CH2Cl2): n(CO) 2088w, 2078s, 2045s, 2031s, 2003vs, 1988sh, 1970w cm1. 1H NMR (C6D6) d 7.99e8.05 (m, 4H, Ph), 7.81e7.84 (m, 4H, Ph), 7.67 (d, 2H, Ph), 7.61 (d, 2H, Ph), 6.87e7.14 (m, 18H, Ph)?7.39 (s, 1H, OsH). 13C{1H} NMR (CDCl3): d (CO) 190.85 (1C), 190.28 (1C), 189.01 (1C), 187.98 (1C), 178.61 (1C), 173.61 (1C), 173.58 (1C), 172.13 (1C), 170.74 (1C); d (Ph) 137.76, 137.62, 137.57, 135.19, 134.94, 134.78, 134.75, 134.36, 130.89, 130.32, 129.98, 129.85, 129.80, 129.74, 129.68, 129.34, 129.05, 128.94, 128.84, 128.65, 128.56, 127.76, 127.73, 127.54. Anal. Calcd for C45H31O9Cl2Os3Sb3: C 31.38, H 1.81. Found: C 30.95, H 1.71. ESI-MSþ (m/z): 1687 [M-Cl]þ, 1659 [M-Cl-CO]þ. Cluster 6b: Rf ¼ 0.65. Yield ¼ 14 mg (67%). IR (CH2Cl2): n(CO)

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2087w, 2077s, 2042s, 2030s, 2002vs, 1982m cm1. 1H NMR (C6D6) d 7.83e7.89 (m, 8H, Ph), 7.71 (d, 2H, Ph), 7.63 (d, 2H, Ph), 6.93e7.12 (m, 18H, Ph), 1.97 (s, broad, 1H, SbOH)?7.47 (s, 1H, OsH). ESI-MSþ: 1687 [M-OH]þ, 1668 [M-Cl]þ. 4.7. Reaction of 4a with I2 Cluster 4a (40 mg, 24 mmol) was dissolved in THF (20 ml) and I2 (6.5 mg, 26 mmol) was added to the above solution. The resulting mixture was stirred at room temperature for 15 h, resulting in an orange solution. The solvent was removed and the residue separated by TLC, with DCM/hexane (1:1, v/v) as the eluent, to give one major band of mer-7a. Rf ¼ 0.65. Yield ¼ 26 mg (70%). IR (CH2Cl2): n(CO) 2102w, 2089w, 2054w, 2040w, 2014s, 1977w cm1. 1H NMR (C6D6) d 7.81e7.83 (m, 4H, Ph), 7.67e7.69 (m, 4H, Ph), 6.97e7.10 (m, 12H, Ph). 13C{1H} NMR (CDCl3): d (CO) 182.63 (2C), 182.61 (2C), 176.53 (2C), 171.41 (1C), 169.23 (2C); d (Ph) 135.42, 135.04, 131.01, 130.16, 129.88, 129.10, 128.70, 127.61. Anal. Calcd for C33H20O9ClIOs3Sb2: C 25.79, H 1.31. Found: C 26.13, H 1.43. ESI-MSþ (m/z): 1556 [MþH2OþH]þ, 1502 [M-Cl]þ. 4.8. Conversion of mer-7a to fac-7a Cluster mer-7a (20 mg, 12.8 mmol) was dissolved in dry THF (10 ml). After three cycles of freeze-pump-thaw, the solution was heated at 65  C and monitored by IR spectroscopy. After 20 h, the solvent was removed in vacuo and the residue separated by TLC, with DCM/hexane (1:1, v/v) as the eluent, to give two bands. Band 1 was identified as unreacted mer-7a. Rf ¼ 0.65. Yield ¼ 9 mg (45%). Band 2 was identified as fac-7a. Rf ¼ 0.60. Yield ¼ 9 mg (45%). IR (CH2Cl2): n(CO) 2098w, 2081s, 2049s, 2009m cm1. 1H NMR (C6D6) d 7.88e7.90 (m, 4H, Ph), 7.47e7.49 (m, 4H, Ph), 6.95e7.11 (m, 12H, Ph). 13C{1H} NMR (CDCl3): d (CO) 176.62 (2C), 173.48 (2C), 173.01 (2C), 170.78 (1C), 170.34 (2C); d (Ph) 136.74, 135.41, 132.06, 131.91, 129.66, 128.75, 128.66. Anal. Calcd for C33H20O9ClIOs3Sb2: C 25.79, H 1.31. Found: C 26.18, H 1.44. ESI-MSþ (m/z): 1502 [M-Cl]þ, 1474 [M-Cl-CO]þ, 1446 [M-Cl-2CO]þ, 1418 [M-Cl-3CO]þ. 4.9. Reaction of 4b with I2 Cluster 4b (40 mg, 24 mmol) was dissolved in THF (20 ml) and I2 (6.0 mg, 24 mmol) was added to the above solution. The resulting mixture was stirred at room temperature for 36 h, resulting in an orange-yellow solution. The solvent was removed and the residue separated by TLC, with DCM/hexane (1:3, v/v) as the eluent, to give two bands. Band 1 was identified as mer-7b. Rf ¼ 0.45. Yield ¼ 10 mg (28%). IR (CH2Cl2): n(CO) 2077m, 2046m, 2029w, 2005s, 1977w cm1. 1H NMR (C6D6) d 7.84 (d, 4H, Ph), 7.70 (d, 4H, Ph), 6.98e7.11 (m, 12H, Ph), 6.12 (s, 1H, OsH). Band 2 was identified as fac-7b. Rf ¼ 0.40. Yield ¼ 8 mg (22%). IR (CH2Cl2): n(CO) 2075s, 2046s, 2028w, 2006m cm1. 1H NMR (C6D6) d 7.91 (d, 4H, Ph), 7.68 (d, 4H, Ph), 6.97e7.12 (m, 12H, Ph), 8.73(s, 1H, OsH). 4.10. Crystallographic analyses Single crystals were obtained by slow evaporation from solution. X-ray diffraction intensity data were collected on a Bruker Kappa diffractometer equipped with a CCD detector, employing Mo Ka radiation (l ¼ 0.71073 Å), with the SMART suite of programs [11]; data were processed and corrected for Lorentz and polarization effects with SAINT [12], and for absorption effects with SADABS [13]. For cluster fac-7b, the intensity data were collected on a

SuperNova (Dual source) Agilent diffractometer using Mo Ka radiation (l ¼ 0.71073 Å); the data was processed and corrected for absorption effects with CrysAlisPro [14]. All the structural solutions and refinements were carried out with the SHELXTL suite of programs [15]. Disorder of the main molecule was observed in 3d, 4a and 6b. For 3d, the molecule was located on a special position (C2) which corresponded to disorder of the molecule about this axis. One of the phenyl ring also exhibited disorder which was modelled with two sites of equal occupancy. Disorder of two phenyl rings were also observed in 4a and 6b, which were modelled in the same manner as above. The metal hydride in 6b was not located directly from the X-ray data but was placed by potential energy calculations using the XHYDEX program [16], and then refined with a riding model. In addition, a large residue was interpreted as a Cl atom with partial occupancy; this corresponded to the presence of 6a, and refined to ~17%. Solvent molecules were located in 4a, 7a and 7b; a hexane solvate with partial occupancy and disordered about an inversion centre for 4a, a disordered DCM solvate modelled with two sites of equal occupancy for 7a, and two hexane solvates, one located on an inversion centre for 7b. Organic hydrogen atoms were placed in calculated position. All non-hydrogen atoms were refined with anisotropic thermal parameters in the final model. Crystal data, data collection parameters, and refinement data are summarized in Supporting Information Table S1. 4.11. Computational studies DFT calculations were performed with the Gaussian 09W suite of programs [17]. Becke's three-parameter hybrid function and LeeYangParr's gradient-corrected correlation function (B3LYP) [18] was employed; the Los Alamos effective core potential doublez (LANL2DZ) basis set [19], together with d- or f-type polarization functions [20], is employed for the Os, Sb and I atoms, while the 6311þG(2d, p) basis set is used for the remaining atoms. Spinrestricted calculations were used for all geometry optimizations. Harmonic frequencies were then calculated to characterize the stationary points as equilibrium structures with all real frequencies, and to evaluate zero-point energy (ZPE) corrections. Acknowledgement This work was supported by Nanyang Technological University and the Ministry of Education (Research Grant No. M4011158). Y.-Z. Li thanks the university for a Research Scholarship. We also acknowledge Dr. Yan-Li Zhao for the use of his X-ray diffractometer and Dr. Pei-Zhou Li for assistance with the data collection on fac-7b. Appendix A. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jorganchem.2016.03.025. References [1] (a) E. Zangrando, M. Casanova, E. Alessio, Chem. Rev. 108 (2008) 4979e5013; (b) P. Thanasekaran, C.-C. Lee, K.-L. Lu, Acc. Chem. Res. 45 (2012) 1403e1418; ~ o, E. Pía, M.D. García, V. Blanco, A. Fern (c) C. Alvarin andez, C. Peinador, J.M. Quintela, Chem. Eur. J. 19 (2013) 15329e15335; (d) M. Ponce-Vargas, Chem. Open 4 (2015) 656e660; (e) B. Jiang, J. Zhang, J.-Q. Ma, W. Zheng, L.-J. Chen, B. Sun, C. Li, B.-W. Hu, H. Tan, X. Li, H.-B. Yang, J. Am. Chem. Soc. 138 (2016) 738e741. [2] (a) R.D. Ernst, T.J. Marks, J.A. Ibers, J. Am. Chem. Soc. 99 (1977) 2090e2098; (b) W.K. Leong, R.K. Pomeroy, R.J. Batchelor, F.W.B. Einstein, C.F. Campana, Organometallics 16 (1997) 1079e1082; (c) D. Fenske, A. Rothenberger, S. Wieber, Eur. J. Inorg. Chem. 2007 (2007)

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