Metal-Only Lewis Pairs Based on Zerovalent Osmium - ACS Publications

Article pubs.acs.org/Organometallics

Metal-Only Lewis Pairs Based on Zerovalent Osmium Robin Bissert, Holger Braunschweig,* Rian D. Dewhurst, and Christoph Schneider Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074 Würzburg, Germany S Supporting Information *

ABSTRACT: A series of zerovalent osmium carbonyl complexes have been treated with Lewis acids GaCl3 and Ag+ to gauge their Lewis basicity. Additionally, comparisons are made between these osmium compounds and analogous iron and ruthenium carbonyl complexes by transfer reactions. This allows direct comparison of the group 8 carbonyl complexes to each other and the establishment of a trend of their Lewis basicity.

■

INTRODUCTION Although transition metals are generally thought of as Lewis acidic and electron accepting in nature (from ligands, for example), the idea of transition-metal fragments acting as Lewis bases is far from new. Early work in this area from Vaska, Collman, Werner, Shriver, and others linked transition-metal Lewis basicity to the ability of a metal fragment to break bonds and, by extension, act as catalysts.1 To our knowledge, the first clear mention of metal to ligand dative bonding is contained in a report by Coffey, Lewis, and Nyholm from 1964;2 however, the first unambiguous structural proof for a complex containing an unsupported metal to ligand dative bond was reported by Nowell and Russell three years later.3 Despite these early reports and the clear importance of the concept of metal basicity to other areas of chemistry, reports of complexes containing metal to metal or metal to ligand dative bonds remained infrequent for some time. A few decades later, there are now clear signs that metal to ligand dative bonding is becoming more widely accepted and more frequently recognized. Examples of complexes reported as having metal to element dative interactions supported by bridging ligand scaffolds are now too numerous to comprehensively list, thanks to extensive work from the groups of Hill, Bourissou, Parkin, Owen, Peters, Wass and many others.4−6 Unsupported metal-only Lewis pairs (MOLP), which lack stabilizing bridging ligand scaffolds, rely solely on the M→ E/M bond to maintain complex stability. While such unsupported MOLPs can be understood as pure representations of this dative bonding, they are considerably less well represented in the literature.7 Beginning around 2007, we became interested in unsupported metal−metal dative bonding, leading to the publication of our 2012 article in Chemical Reviews, which we hoped would stimulate discussion and research into unsupported MOLPs. Since the publication of this review, we have expanded the range of MOLP complexes,8 and encouragingly, a number of other groups have reported MOLPs in their own work, such as those of Jones and Stasch,9 Krossing,10 Rivard,11 Itazaki and Nakazawa,12 Figueroa,13 Kaltsoyannis and Mountford,14 and Shionoya.15 With these studies, nascent applications of MOLPs have been uncovered: © XXXX American Chemical Society

(1) metal to metal dative bonding interactions have been shown to activate the Lewis base metal fragment toward ligand binding,13 and (2) M→M dative bonds have been used to promote host−guest interactions in the cavity of a designed host molecule.15 The Lewis basicity of group 8 metal complexes has been a major contributor to the early work in the field of MOLPs, with the group of Pomeroy and Einstein presenting a wide range of complexes containing dative bonds from group 8 bases to Lewis acidic transition-metal fragments such as group 6 ML5, group 7 MXL4, group 8 MX2L3, and even tandem MOLPs of the form L5M→ML4→M′L5 (M = group 8, M′ = group 6).16 Alongside this, a number of groups have reported both supported and unsupported MOLPs using group 8 metal bases and late TM Lewis acids.17 Over the past few years we have been interested in exploring MOLPs constructed from zerovalent group 8 Lewis bases and main-group Lewis acids, examining the effects of a changing ligand set on the donating abilities of the metals.8c,d,g,h Notably, Lewis acid transfer reactions were performed between group 8 complexes with differing ligand sets. These studies have pointed to a distinctly superior donating ability of Ru over Fe Lewis bases, while the zerovalent Pt complex [Pt(PCy3)2] was found to be superior to all of the group 8 complexes. When the metal was kept constant, increased donor ability was observed with successive replacement of CO with phosphine ligands. Interestingly, replacement of phosphines with more strongly donating NHC ligands led to complexes with roughly equivalent donor strengths. In order to complete the study of MOLPs based on zerovalent group 8 metal donors, we embarked on a study using zerovalent osmium complexes with the main-group Lewis acid gallium trichloride. These results are presented herein.

■

RESULTS AND DISCUSSION Synthesis of Tetracarbonyl Os→Ga MOLPs. The synthesis of [Os(CO)4(PMe3)] (1a) was carried out on the basis of the literature procedure of Martin, Einstein, and Received: June 16, 2016

A

DOI: 10.1021/acs.organomet.6b00495 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Pomeroy18 using [Os3(CO)12] and 3 equiv of PMe3 in an autoclave under a CO pressure of 130 bar and 230 °C. After 3 days 1a was isolated after sublimation as a colorless crystalline solid (60%). [Os(CO)4IMes] (1b) could be synthesized without the aid of an autoclave at normal pressure by stirring [Os 3 (CO) 12 ] with 3 equiv of IMes (1,3-bis(2,4,6trimethylphenyl)imizadol-2-ylidene) in THF for 24 h at 75 °C. After isolation and recrystallzation, 1b was obtained as a light yellow solid in moderate yield (52%). To the best of our knowledge, there exists no comparable osmium carbonyl complex bearing a single NHC ligand (for single-crystal X-ray structure and spectroscopic data see the Supporting Information). Both compounds were dissolved separately in benzene and treated with 1 equiv of GaCl3 to form the Lewis adducts 2a,b in acceptable yields as colorless solids (2a, 86%; 2b, 41%) (Figure 1).

Figure 2. Crystallographically derived structures of MOLPs 2a,b. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms, solvent molecules, and some ellipsoids have been omitted for clarity. Selected bond lengths (pm) and angles (deg): for 2a, Os1−P1 242.1(2), Os1−Ga1 257.4(1); P1−Os1−Ga1 92.16(5); for 2b, Os1− C5 218.9(5), Os1−Ga1 257.5(2); C5−Os1−Ga1 178.01(11).

(both 0.95) and smaller than those of the iron analogues with identical ligand sets (0.98, 0.99).8c,d,g,h This leads to the assumption that the osmium carbonyl complexes could be stronger Lewis bases than the analogous iron complexes but weaker than the analogous ruthenium carbonyl complexes; however, the differences here are very small. Synthesis of Tricarbonyl Os→Ga MOLPs. In order to increase the Lewis basicity of osmium carbonyl complexes used in the syntheses of 2a,b, we targeted tricarbonyl complexes of the form [Os(CO)3L2]. In order to achieve this, [Os3(CO)12] was treated with 6 equiv of PMe3 under conditions analogous to those for 1a to obtain the complex [Os(CO)3(PMe3)2] (1c). After sublimation, 1c was obtained in moderate yield (58%) as a crystalline colorless solid. Additionally, the complex [Os(CO)3(PMe3)(IMes)] (1d) was synthesized by irradiation of 1b with 1 equiv of PMe3 and was isolated after workup as a colorless solid in good yield (84%) (for single-crystal X-ray structure and spectroscopic data, see the Supporting Information). The reactions of benzene solutions of 1c,d with 1 equiv of GaCl3 led to the Lewis adducts [(Me3P)2(OC)3Os→ GaCl3] (2c) and [(IMes)(Me3P)(OC)3Os→GaCl3] (2d), which could be isolated after recrystallization from CH2Cl2 in good yields (2c, 74%; 2d, 70%) (Figure 3). The 31P{1H} NMR spectra of 1c,d show signals at δ −49.4 (1c) and δ −46.4 (1d), respectively, which are shifted to frequencies higher than those of the Lewis adducts (2c, δ −55.7; 2d, δ −60.3). The solution IR spectra of both Lewis adducts show two carbonyl stretching bands (2c, 2086, 2015 cm−1; 2d, 2081, 2007 cm−1), which led to the assumption of a fac geometry of the three carbonyls. In contrast, however, a single-crystal X-ray diffraction study of 2c,d revealed that the donor ligands are situated mutually trans, with the GaCl3 and three carbonyls in one plane (Figure 4).

Figure 1. Synthesis of [Os(CO)4(PMe3)] (1a), [Os(CO)4(IMes)] (1b), cis-[(Me 3 P)(OC) 4Os→GaCl3 ] (2a), and trans-[(IMes)(OC)4Os→GaCl3] (2b).

The 31P{1H} NMR spectrum of 2a shows a singlet at δ −55.2 shifted to frequency lower than that of 1a (δ −52.6). The solution IR spectrum shows four stretching bands for the carbonyls (2060, 1971, 1945, 1932 cm−1), which is in agreement with an octahedral cis conformation of the adduct. Single-crystal X-ray diffraction analysis of 2a confirmed the structure suggested by IR spectroscopy. The molecular structure shows an octahedral Os center with the GaCl3 cis to the PMe3 donor ligand with an Os−Ga bond distance of 257.4(1) pm. In contrast, the IR spectrum of 2b shows only one stretching band, which could be explained by a trans geometry. X-ray diffraction of suitable single crystals confirmed this assumption, showing the GaCl3 to be trans to the IMes donor. The Os−Ga distance of 2b (257.5(2) pm) is equivalent to that of 2a within experimental uncertainty (Figure 2). Both Os−Ga bond lengths are slightly longer than the values of the analogous ruthenium carbonyl compounds [(L)(OC)4Ru→GaCl3] (L = PMe3, 254.7(1) pm; L = IMes, 254.1(2) pm). The nearly identical covalent radii of osmium (144 pm) and ruthenium (146 pm) make a direct comparison of the bond lengths possible; however, a direct comparison with iron carbonyl adducts is not possible due to its somewhat smaller covalent radius (132 pm).19 Therefore, the relative distance (drel) is used for comparisons, which is the quotient of the experimental M−M distance and the sum of the covalent radii. The drel values of 2a,b (both 0.97) are only slightly larger than those of the ruthenium analogues with identical ligand sets B

DOI: 10.1021/acs.organomet.6b00495 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

with 0.5 equiv of [AgBArCl4] under exclusion of light. After isolation and recrystallization from CH2Cl2 the adduct [{(Me3P)2(OC)3Os}2(μ-Ag)][BArCl4] (2e) was obtained as a white solid in moderate yield (∼57%) (Figure 5).

Figure 5. Synthesis of [{(Me3P)2(OC)3Os}2(μ-Ag)][BArCl4] (2e).

Figure 3. Synthesis of [Os(CO)3(PMe3)2] (1c), [Os(CO)3(IMes)(PMe3)] (1d), mer,trans-[(Me3P)2(OC)3Os→GaCl3] (2c), and mer[(IMes)(PMe3)(OC)3Os→GaCl3] (2d).

Complex 2e shows one signal at δ −55.8 in the 31P{1H} NMR spectrum, which is shifted to lower frequency in comparison to that of the starting material (1c, δ −49.4). The solution IR spectrum reveals three carbonyl stretching bands, which is consistent with a mer,trans conformation. The molecular structure in the solid state was confirmed by X-ray diffraction analysis, which shows both donor ligands situated mutually trans and the two osmium tricarbonyl fragments to be bridged by the silver cation (Figure 6).

Figure 6. Crystallographically derived structure of MOLP 2e. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms, solvent molecules, counterions, and some ellipsoids have been omitted for clarity. Selected bond lengths (pm) and angles (deg) for 2e: Os1− Ag1 272.3(1), Os2−Ag1 272.5(1), C1−Ag1 290.1(3), C3−Ag1 283.2(3), C4−Ag1 277.5(3), C6−Ag1 297.1(3), P1−Os1−P2 178.7(1), P3−Os2−P4 175.0(1), Os1−Ag1−Os2 174.7(1), P1− Os1−P2 fragment vs P3−Os2−P4 fragment 74.8(2).

Figure 4. Crystallographically derived structures of MOLPs 2c,d. Ellipsoids are drawn at the 50% probability level. Hydrogen atoms, solvent molecules, and some ellipsoids have been omitted for clarity. Selected bond lengths (pm) and angles (deg): for 2c, Os1−P1 238.9(1), Os1−P2 239.4(1), Os1−Ga1 256.3(1); P1−Os1−P2 176.7(1); for 2d, Os1−C4 214.3(4), Os1−P1 240.6(1), Os1−Ga1 257.3(1); C4−Os1−P1 177.8(1).

Complex 2e possesses a geometry similar to that of the recently reported ruthenium and iron analogues.8c,g,10 The Os− Ag bond distance of 2e (drel 0.94) also lies between that of the analogous iron (drel 0.95) and ruthenium (drel 0.93) carbonyl complexes, which confirms the observed trend of the Lewis basicity in these GaCl3 adducts. The two osmium carbonyl fragments of 2e are staggered with respect to each other (angle between P1−P2 and P3−P4 axes 74.8(2)°), to a slightly lesser degree than in the iron and ruthenium analogues (both 88.9(2)°). One carbonyl of each fragment lies on the Os1− Ag1−Os2 axis, and the two other carbonyls of each fragment show relatively close contacts with the silver cation (C1−Ag1 290.1(3) pm, C3−Ag1 283.2(3) pm, C4−Ag1 277.5(3) pm, C6−Ag1 297.1(3) pm). However, the CO ligands are nearly unperturbed, with effectively linear Os−C−O axes, which argues against any appreciable Ag−C interaction. This is in agreement with similar interactions of the analogous iron and ruthenium complexes as well as with the aforementioned

These solid-state molecular structures are in contrast to the observed stretching bands in the IR spectra, which can only be explained by the presence of overlapping signals. The Os−Ga distances of 2c,d (2c, 256.3(1) pm; 2d, 257.3(1) pm) lie in the same range as those of the tetracarbonyl complexes (2a, 257.4(1) pm; 2b, 257.5(2) pm). Comparisons to the analogous iron and ruthenium compounds [L(Me3P)(OC)3M→GaCl3] (L = PMe3, M = Fe, drel 0.97; L = IMes, M = Fe, drel 0.98; L = PMe3, IMes, M = Ru, drel 0.95) show that the drel values of the osmium carbonyl complexes (2c, drel 0.96; 2d, drel 0.97) are again between those of Fe and Ru complexes, reiterating the trend observed with the tetracarbonyl complexes. Synthesis of a Tricarbonyl Os→Ag MOLP. In 2014, the Krossing group reported the synthesis of a double Fe adduct of Ag+, [{(OC)5Fe}2(μ-Ag)],10 which was followed closely by our report of a very similar (Fe→)2Ag+ complex, in addition to a bis(platinum) derivative.8c In an attempt to extend this reactivity to osmium, the tricarbonyl complex 1c was treated C

DOI: 10.1021/acs.organomet.6b00495 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

Figure 7. Transfer of the Lewis acid GaCl3 from iron to ruthenium or osmium carbonyl complexes and then to [Pt(PCy3)2], as shown in current and previous work.

(Fe→)2Ag+ adduct of Krossing.10 The Os−Ag distances of 2e (272.3(1), 272.5(1) pm) are also only slightly longer than that in a comparable monoosmium MOLP [(Ph3P)2(OC)3Os→ AgOTf] (271.2(1) Å), which contains a similar orientation of the two proximal Os−CO units toward the Ag atom.17c Lewis Acid Transfer Reactions and Comparisons to Iron and Ruthenium MOLPs. On the basis of the M−Ga and M−Ag bond distances, one can tentatively infer a trend of the strength of the Lewis basicity of the base fragments. However, without further evidence, no qualitative conclusion can be made, given the many other factors that influence the M−M bond distance, such as the steric demand of the ligands. Therefore, transfer experiments among analogous iron, ruthenium, and osmium carbonyl complexes have been carried out to gauge the Lewis basicity of these complexes. Accordingly, 2a and 1c were dissolved in equimolar amounts in CD2Cl2 and the resulting mixture was monitored by 31P{1H} NMR spectroscopy, showing complete transfer of the Lewis acid from the monosubstituted to the disubstituted complex. In contrast, when samples of 2c and 1a were mixed, no transfer was observed. This behavior is in agreement with similar experiments in our recent studies of iron and ruthenium carbonyl complexes.8d,g,h Transfer experiments between iron and osmium carbonyl complexes have shown that the GaCl3 unit of [(Me3P)2(OC)3Fe→GaCl3] could be transferred even to both 1a and 1c, as monitored by 31P{1H} NMR spectroscopy. A similar transfer was also observed from analogous iron MOLPs to their corresponding ruthenium carbonyl analogues. On the basis of these transfer experiments and on the M−Ga bond lengths we can comfortably say that osmium carbonyl complexes are more Lewis basic than iron carbonyl complexes. It is also worth noting that the transfers from [(Me3P)2(OC)3Fe→GaCl3] to Os complexes 1a and 1c were relatively slow (∼3 days for completion), while the reaction between Os complexes 2a and 1c was significantly faster (∼2 h for completion). This suggests that the basicityincreasing effect of adding additional phosphine ligands is greater than that of changing the metal from iron to osmium. Comparisons between osmium and ruthenium were also carried out by transfer reactions. We treated a solution of 2c in CD2Cl2 with an equimolar amount of [(Me3P)2(OC)3Ru] and also of 1c with [(Me3P)2(OC)3Ru→GaCl3] and monitored the reactions again by 31P{1H} NMR spectroscopy. In both cases we could observe an incomplete transfer of the Lewis acid, indicating the Lewis basicity of ruthenium and osmium carbonyl complexes with the same ligand environments being

approximately equal (Figure 7). It should also be noted that the observed equivalence of the Ru and Os bases is somewhat in contrast with Norton’s measurements of the Brønsted acidity of the group 6 hydrides [(η5-C5H5)M(CO)3H] and dihydrides [M(CO)4H2] (M = Fe, Ru, Os),20 and Angelici’s measurements of the heats of protonation of divalent group 6 complexes.21 Both of these studies implied increasing basicity as group 8 is descended, with Os complexes being better Brønsted bases than their Ru counterparts. Transfers between 1c,d and their gallium adducts showed no transfer of the Lewis acid. One might assume that with a better σ-donor ligand such as IMes the complex should be a better Lewis base; however, it seems that the difference between 1c and 1d is not large enough to induce the transfer of the GaCl3. This is in agreement with our study of analogous ruthenium carbonyl complexes.8g We also compared the Lewis basicity of osmium carbonyl complexes with that of the well-known transition-metal Lewis base [Pt(PCy3)2], which led to not only transfer of the GaCl3 unit to Pt0 but also decomposition. Thereby, we combined the silver adduct 2e and 2 equiv of the Pt0 compound in C6H5F to avoid decomposition of the platinum complex. The reaction was also monitored by 31P{1H} NMR spectroscopy, and we observed rapid transfer of the Lewis acid from osmium to platinum but no transfer between 1c and [{(Cy3P)2Pt}2(μ-Ag)]. Thus, overall, it is clear that this Pt0 compound is more Lewis basic than all group 8 carbonyl complexes studied. However, when the Lewis basicities of zerovalent group 8 complexes are compared with those of zerovalent group 10 complexes, the thermodynamic cost of rearrangement of the former from trigonal bipyramidal to octahedral should also be considered. The required rearrangement of the former complexes constitutes somewhat of a handicap to their basicity relative to linear [Pt0L2] complexes, which require little deformation to accommodate a Lewis acid.

■

CONCLUSIONS Herein we have presented the Lewis basicity of osmium carbonyl complexes and their comparison to analogous iron and ruthenium carbonyl complexes. We included osmium in our studies in order to both complete group 8 and examine if the observed trend of the Lewis basicity in iron and ruthenium carbonyl complexes would be continued in their osmium analogues. On the basis of the M−Ga bond lengths and transfer reactions we can say that the Lewis basicity increases from iron to ruthenium or osmium but the Lewis basicities between D

DOI: 10.1021/acs.organomet.6b00495 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

NMR (400.1 MHz, CD2Cl2, 297 K): δ 2.11 (d, 2JHP = 10 Hz, 9H, CH3). 31P{1H} NMR (162.0 MHz, CD2Cl2, 297 K): δ −55.2 (s). Anal. Calcd for C7H9Cl3GaOsO4P: C, 15.16; H, 1.64. Found: C, 15.23; H, 2.05. Synthesis of trans-[(IMes)(OC)4Os→GaCl3] (2b). A solution of 1b (40.0 mg, 65.8 μmol) in 5 mL of Et2O was treated with GaCl3 (6.0 mg, 65.8 μmol). The mixture was left to stand for 6 h. The resulting white precipitate was filtered off and washed with benzene (2 × 2 mL) and pentane (2 × 2 mL). The residue was recrystallized from C6H5F at −30 °C to yield 2b (21.6 mg, 26.8 μmol, 41%) as a colorless crystalline solid. IR (CH2Cl2): 2044 (νCO) cm−1. 1H NMR (400.1 MHz, CD2Cl2, 297 K): δ 2.05 (s, 12H, CH3), 2.39 (s, 6H, CH3), 7.14 (s, 4H, CHAr), 7.44 (s, 2H, CHImid). 13C{1H} NMR (100.6 MHz, CD2Cl2, 297 K): δ 17.9 (s, 4C, CH3), 21.3 (s, 2C, CH3), 126.2 (s, 2C, CHImid), 130.8 (s, 4C, CHAr), 135.5 (s, 4C, Cq), 136.4 (s, 2C, Cq), 142.7 (s, 2C, Cq), 151.3 (s, 1C, CImid ), 172.8 (s, 4C, CO). Anal. Calcd for C25H24Cl3GaN2OsO4.(C6H5F): C, 42.36; H, 3.33; N, 3.19. Found: C, 42.86; H, 3.39; N, 3.21. Synthesis of [Os(CO)3(PMe3)2] (1c).16i,24 A procedure similar to that used for the preparation of 1a was applied by using [Os3(CO)12] (1.00 g, 1.10 mmol) and PMe3 (0.70 mL, 0.52 g, 6.6 mmol) to provide the crude product. The residual solid was then sublimed at 1 × 10−3 mbar at 70 °C to yield the product (817 mg, 1.92 mmol, 58%) as a colorless solid. IR (CH2Cl2): 1873 (νCO) cm−1. 1H NMR (400.1 MHz, C6D6, 297 K): δ 1.79 (t, 2JHP = 8 Hz, 18H, CH3). 31P{1H} NMR (162.0 MHz, CD2Cl2, 297 K): δ −49.4 (s). Synthesis of [Os(CO)3(IMes)(PMe3)] (1d). A solution of [Os(CO)4(IMes)] (1b; 200 mg, 0.33 mmol) in 50 mL of benzene was treated with PMe3 (0.03 mL, 25.1 mg, 0.33 mmol). The mixture was irradiated in front of a mercury lamp for 5 h, and then the solvent was removed under reduced pressure. The residue was recrystallized in toluene at −30 °C to afford 1d (185 mg, 0.28 mmol, 84%) as a colorless crystalline solid. IR (CH2Cl2): 1853 (νCO) cm−1. 1H NMR (500.1 MHz, C6D6, 297 K): δ 1.18 (d, 2JHP = 10 Hz, 9H, CH3), 2.14 (s, 12H, CH3), 2.24 (s, 6H, CH3), 6.11 (s, 2H, CHImid), 6.86 (s, 4H, CHAr). 13C{1H} NMR (125.8 MHz, C6D6, 297 K): δ 18.8 (s, 4C, CH3), 20.4 (d, 1JCP = 36 Hz, 3C, CH3), 21.2 (s, 2C, CH3), 122.5 (d, 4 JCP = 2 Hz, 2C, CHImid), 129.7 (s, 4C, CH), 136.4 (s, 4C, Cq), 138.5 (s, 2C, Cq), 138.8 (s, 2C, Cq), 164.2 (d, 2JCP = 59 Hz, 1C, CImid), 201.9 (d, 2JCP = 13 Hz, 3C, CO). 31P{1H} NMR (202.5 MHz, C6D6, 297 K): δ −46.4 (s); Anal. Calcd for C27H33OsN2O3P: C, 49.53; H, 5.08; N, 4.28. Found: C, 49.64; H, 4.92; N, 3.93. Synthesis of mer,trans-[(Me3P)2(OC)3Os→GaCl3] (2c). A procedure similar to that used for the preparation of 2a was applied by using [Os(CO)3(PMe3)2] (1c; 20.0 mg, 46.9 μmol) and GaCl3 (8.26 mg, 46.9 μmol) to provide 2c (21.0 mg, 35.1 μmol, 74%) as a colorless crystalline solid. Due to poor solubility no 13C{1H} NMR could be measured. IR (CH2Cl2): 2086, 2015 (νCO) cm−1. 1H NMR (400.1 MHz, CD2Cl2, 297 K): δ 2.07 (vt, N = |2JHP + 4JHP| = 8 Hz, 18H, CH3). 31P{1H} NMR (162.0 MHz, CD2Cl2, 297 K): δ −55.7 (s). Anal. Calcd for C9H18Cl3GaOsO3P2: C, 17.94; H, 3.01. Found: C, 18.07; H, 3.18. Synthesis of mer,trans-[(IMes)(Me3P)(OC)3Os→GaCl3] (2d). A procedure similar to that used for the preparation of 2a was applied by using [Os(CO)3(PMe3)(IMes)] (1d; 15.0 mg, 22.9 μmol) and GaCl3 (4.00 mg, 22.9 μmol). After isolation and recrystallization in C6H5F, 2d (13.3 mg, 16.1 μmol, 70%) was obtained as a colorless crystalline solid. IR (CH2Cl2): 2081, 2007 (νCO) cm−1. 1H NMR (500.1 MHz, CD2Cl2, 297 K): δ 1.81 (d, 2JHP = 10 Hz, 9H, CH3), 2.23 (s, 12H, CH3), 2.38 (s, 6H, CH3), 7.09 (s, 4H, CHAr), 7.25 (s, 2H, CHImid). 13 C{1H} NMR (125.8 MHz, CD2Cl2, 297 K): δ 18.9 (d, 1JCP| = 40 Hz, 3C, CH3), 19.4 (s, 4C, CH3), 21.2 (s, 2C, CH3), 125.8 (s, 2C, CHImid), 130.8 (s, 4C, CH), 136.9 (s, 2C, Cq), 137.3 (s, 4C, Cq), 142.0 (s, 2C, Cq), 155.4 (d, 2JCP = 55 Hz, 1C, CImid), 174.0 (s, 1C, CO), 178.5 (d, 2 JCP = 10 Hz, 2C, CO). 31P{1H} NMR (202.5 MHz, CD2Cl2, 297 K): δ −60.5 (s); Anal. Calcd for C27H33Cl3GaN2OsO3P.(C6H5F): C, 42.76; H, 4.13; N, 3.02. Found: C, 42.95; H, 4.36; N, 2.81. Synthesis of [{(Me3P)2(OC)3Os}2(μ-Ag)][BArCl4] (2e). To a solution of 1c (20.0 mg, 46.9 μmol) in 3 mL of benzene was slowly added a solution of [AgBArCl4] (16.5 mg, 23.5 μmol) in 2 mL of

ruthenium and osmium carbonyl complexes are effectively equivalent.

■

EXPERIMENTAL SECTION

General Information. All syntheses were performed under an inert atmosphere of dry argon using standard Schlenk techniques or in a glovebox (MBraun). Pentane, hexane, benzene, toluene, fluorobenzene, THF, and CH2Cl2 were dried by distillation over potassium (benzene, toluene), Na/K alloy (hexane, THF), or phosphorus pentoxide (fluorobenzene, CH2Cl2) under argon and stored over molecular sieves (4 Å). C6D6 and CD2Cl2 were degassed by several freeze−pump−thaw cycles and stored over molecular sieves. The NMR spectra were recorded on a Bruker AMX 400 (1H, 400.1 MHz; 13 C, 100.6 MHz; 11B, 128.4 MHz; 31P, 162.0 MHz) and/or a Bruker Avance 500 FT-NMR spectrometer (1H, 500.1 MHz; 13C, 125.8 MHz; 11 B, 160.5 MHz; 31P, 202.5 MHz). Chemical shifts are given in ppm and were referenced to external TMS (1H, 13C{1H}), [BF3·OEt2] (11B{1H}), and 85% H3PO4 (31P{1H}), and coupling constants are given in Hz. Elemental analyses were obtained with an Elementar Vario MICRO cube instrument. Infrared spectra were measured on a JASCO FT/IR-6200 type A spectrometer. The light source for photochemical experiments was a Hg/Xe arc lamp (400−550 W) equipped with IR filters, with irradiation at 210−600 nm. Trimethylphosphine, 22 1,3-dimesitylimidazol-2-ylidene, 23 [Ru(CO) 4 (PMe 3 )], 8g [Ru(CO) 3 (PMe 3 ) 2 ], 8g [(OC) 4 (Me 3 P)Ru→ GaCl3],8g [(OC)3(Me3P)2Ru→GaCl3],3 and Ag[BArCl4]8c were prepared according to literature procedures. [Os3(CO)12] was purchased from Strem Chemicals and GaCl3 from Sigma-Aldrich; both were used without further purification. Synthesis of [Os(CO)4(PMe3)] (1a). The synthesis of 1a was carried out according to a literature method.18 In a 250 mL glass inlay [Os3(CO)12] (2.00 mg, 2.20 mmol) was suspended in 120 mL of hexane; PMe3 (0.70 mL, 6.60 mmol, 0.52 g) was then added, and the inlay was put into an autoclave. Carbon monoxide was then passed into the autoclave until a pressure of 80 bar was reached. After that the solution was heated to 230 °C to obtain a final pressure of around 130 bar. The solution was stirred for 72 h, and after the autoclave was cooled to room temperature, the pressure was released. The yellow solution was transferred to a Schlenk flask, and the solvent was removed under reduced pressure. The residual solid was then sublimed at 1 × 10−3 mbar at 50 °C to provide the product 1a (1.38 g, 3.97 mmol, 60%) as a colorless solid. IR (CH2Cl2): 2057, 1971, 1929 (νCO) cm−1. 1H NMR (400.1 MHz, C6D6, 297 K): δ 1.85 (d, 2JHP = 10 Hz, 9H, CH3). 31P{1H} NMR (162.0 MHz, CD2Cl2, 297 K): δ −52.6 (s). Synthesis of [Os(CO)4(IMes)] (1b). To a suspension of [Os3(CO)12] (500 mg, 0.55 mmol) in 20 mL of THF was slowly added a solution of IMes (503 mg, 1.65 mmol) in 10 mL of THF via a dropping funnel. The mixture was stirred at 75 °C for 24 h, and after it was cooled to room temperature, the solvent was removed under vacuum. The residue was extracted with benzene (3 × 10 mL) and then evaporated to dryness. The crude product was recrystallized from DCM at −30 °C to afford 1b (521 mg, 0.86 mmol, 52%) as a light yellow crystalline solid. IR (CH2Cl2): 2046, 1958, 1914 (νCO) cm−1. 1 H NMR (500.1 MHz, C6D6, 297 K): δ 2.01 (s, 12H, CH3), 2.12 (s, 6H, CH3), 6.06 (s, 2H, CHImid), 6.79 (s, 4H, CHAr). 13C{1H} NMR (125.8 MHz, C6D6, 297 K): δ 18.2 (s, 2C, CH3), 20.9 (s, 4C, CH3), 123.3 (s, 2C, CHImid), 129.8 (s, 4C, CH), 135.8 (s, 2C, Cq), 137.3 (s, 4C, Cq), 139.7 (s, 2C, Cq), 157.8 (s, C, CImid), 191.8 (s, 4C, CO). Anal. Calcd for C25H24OsN2O4: C, 49.49; H, 3.99; N, 4.62. Found: C, 49.59; H, 3.90; N, 4.70. Synthesis of cis-[(Me3P)(OC)4Os→GaCl3] (2a). A solution of 1b (31.0 mg, 88.1 μmol) in 5 mL of benzene was treated with GaCl3 (15.5 mg, 88.1 μmol). The mixture was left to stand for 3 h. The resulting white precipitate was filtered off and washed with benzene (2 × 2 mL) and pentane (2 × 2 mL). The residue was recrystallized from CH2Cl2 at −30 °C to yield 2a (38.8 mg, 74.1 μmol, 86%) as a colorless crystalline solid. Due to poor solubility no 13C{1H} NMR could be measured. IR (CH2Cl2): 2060, 1971, 1945, 1932 (νCO) cm−1. 1H E

DOI: 10.1021/acs.organomet.6b00495 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

Crystal data for 2b: C31H29Cl3FGaN2O4Os, Mr = 878.83, colorless block, 0.267 × 0.195 × 0.136 mm3, monoclinic space group P21/c, a = 11.011(9) Å, b = 22.861(13) Å, c = 13.858(12) Å, β = 107.62(3)°, V = 3324(4) Å3, Z = 4, ρcalcd = 1.756 g·cm−3, μ = 4.913 mm−1, F(000) = 1712, T = 100(2) K, R1 = 0.0497, wR2 = 0.0884, 7031 independent reflections (2θ ≤ 53.594°), and 394 parameters. CCDC 1485953. Crystallographic Details for 2c. The crystal data of 2c were collected on a Bruker D8 Quest diffractometer with a CMOS area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using an intrinsic phasing method (ShelXT), refined with the ShelXLprogram,25 and expanded using Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions. The unit cell contains one solvent molecule ,which has been treated as a diffuse contribution to the overall scattering without specific atom positions by SQUEEZE/PLATON. Crystal data for 2c: C9H18Cl3GaO3OsP2, Mr = 602.44, colorless block, 0.286 × 0.14 × 0.081 mm3, monoclinic space group P21/n, a = 8.9830(12) Å, b = 12.9064(19) Å, c = 19.160(3) Å, β = 97.911(4)°, V = 2200.3(5) Å3, Z = 4, ρcalcd = 1.819 g·cm−3, μ = 7.502 mm−1, F(000) = 1136, T = 100(2) K, R1 = 0.0188, wR2 = 0.0460, 4679 independent reflections (2θ ≤ 53.6°), and 178 parameters. CCDC 1485951. Crystallographic Details for 2d. The crystal data of 2d were collected on a Bruker D8 Quest diffractometer with a CMOS area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using an intrinsic phasing method (ShelXT), refined with the ShelXLprogram,25 and expanded using Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions. The Uii displacement parameters of atoms C40, C41, C42, C43, C44, C45, C50, C51, C52, C53, C54, and C55 were restrained with the ISOR keyword to approximate isotropic behavior. Crystal data for 2d: C39H43Cl3F2GaN2O3OsP, Mr = 1022.99, colorless block, 0.293 × 0.165 × 0.089 mm3, monoclinic space group P21/c, a = 9.926(5) Å, b = 17.865(3) Å, c = 22.965(5) Å, β = 101.65(3)°, V = 3988(2) Å3, Z = 4, ρcalcd = 1.704 g·cm−3, μ = 4.148 mm−1, F(000) = 2024, T = 100(2) K, R1 = 0.0341, wR2 = 0.0662, 8494 independent reflections (2θ ≤ 53.576°), and 506 parameters. CCDC 1485954. Crystallographic Details for 2c. The crystal data of 2e were collected on a Bruker D8 Quest diffractometer with a CMOS area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using an intrinsic phasing method (ShelXT), refined with the ShelXLprogram,25 and expanded using Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions. Crystal data for 2e: C48H53AgBCl8FO6Os2P4, Mr = 1651.46, colorless plate, 0.157 × 0.139 × 0.047 mm3, monoclinic space group P21/c, a = 16.844(5) Å, b = 16.981(3) Å, c = 21.462(6) Å, β = 102.34(2)°, V = 5997(3) Å3, Z = 4, ρcalcd = 1.829 g·cm−3, μ = 5.060 mm−1, F(000) = 3192, T = 100(2) K, R1 = 0.0322, wR2 = 0.0503, 12804 independent reflections (2θ ≤ 53.654°), and 640 parameters. CCDC 1485956.

benzene under exclusion of light. The spontaneous white precipitate was filtered off and washed with benzene (2 × 2 mL) and pentane (2 × 2 mL). The residue was recrystallized from C6H5F at −30 °C to yield 1e (21.1 mg, 13.5 μmol, 57%) as a colorless crystalline solid. IR (CH2Cl2): 2006, 1950, 1923 (νCO) cm−1. 1H NMR (500.1 MHz, CD2Cl2, 297 K): δ 1.91 (vt, N = |2JHP + 4JHP| = 8 Hz, 36H, CH3), 6.99−7.00 (m, 4H, CHAr), 7.02−7.05 (m, 8H, CHAr); 13C{1H} NMR (125.8 MHz, CD2Cl2, 297 K): δ 23.9 (vt, N = |1JCP + 3JCP| = 40 Hz, 12C, CH3), 123.4 (s, 4C, CHAr), 133.3 (q, 3JCB = 4 Hz, 8C, CAr), 133.5 (m, 8C, CHAr), 165.1 (q, 1JCB = 50 Hz, 4C, CAr), 180.0 (td, 2JCAg = 3 Hz, 2JCP = 9 Hz, 2C, CO), 195.4 (td, 2JCAg = 5 Hz, 2JCP = 10 Hz, 4C, CO). 11B{1H} NMR (160.5 MHz, CD2Cl2, 297 K): δ −6.9 (s). 31 1 P{ H} NMR (202.5 MHz, CD2Cl2, 297 K): δ −55.8 (d, 2JPAg = 8 Hz). Anal. Calcd for C42H48AgBCl8Os2O6P4: C, 32.43; H 3.11. Found: C, 32.40; H 3.12. Crystallographic Details for 1b. The crystal data of 1b were collected on a Bruker D8 Quest diffractometer with a CMOS area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using an intrinsic phasing method (ShelXT), refined with the ShelXLprogram,25 and expanded using Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions. Crystal data for 1b: C25H24N2O4Os, Mr = 606.66, colorless block, 0.201 × 0.147 × 0.133 mm3, orthorhombic space group Pnma, a = 15.8145(9) Å, b = 19.413(8) Å, c = 7.594(10) Å, V = 2332(3) Å3, Z = 4, ρcalcd = 1.728 g·cm−3, μ = 5.502 mm−1, F(000) = 1184, T = 100(2) K, R1 = 0.0156, wR2 = 0.0329, 2559 independent reflections (2θ ≤ 53.514°) and 157 parameters. CCDC 1485952. Crystallographic Details for 1d. The crystal data of 1d were collected on a Bruker D8 Quest diffractometer with a CMOS area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using an intrinsic phasing method (ShelXT), refined with the ShelXLprogram,25 and expanded using Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions. The unit cell contains one solvent molecule, which has been treated as a diffuse contribution to the overall scattering without specific atom positions by SQUEEZE/PLATON. The Uii displacement parameters of atom C19 were restrained with the ISOR keyword to approximate isotropic behavior. Crystal data for 1d: C27H33N2O3OsP, Mr = 654.72, colorless block, 0.149 × 0.105 × 0.062 mm3, monoclinic space group C2/m, a = 15.4461(18) Å, b = 12.090(3) Å, c = 16.857(6) Å, β = 95.66(2)°, V = 3132.6(14) Å3, Z = 4, ρcalcd = 1.388 g·cm−3, μ = 4.147 mm−1, F(000) = 1296, T = 121(2) K, R1 = 0.0195, wR2 = 0.0580, 3506 independent reflections (2θ ≤ 53.574°), and 184 parameters. CCDC 1485950. Crystallographic Details for 2a. The crystal data of 2a were collected on a Bruker D8 Quest diffractometer with a CMOS area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using an intrinsic phasing method (ShelXT), refined with the ShelXLprogram,25 and expanded using Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions. Crystal data for 2a: C7H9Cl3GaO4OsP, Mr = 554.38, colorless block, 0.182 × 0.098 × 0.085 mm3, orthorhombic space group Pna21, a = 12.5020(5) Å, b = 8.8053(3) Å, c = 13.5439(5) Å, V = 1490.96(10) Å3, Z = 4, ρcalcd = 2.470 g·cm−3, μ = 10.962 mm−1, F(000) = 1024, T = 100(2) K, R1 = 0.0211, wR2 = 0.0564, 3044 independent reflections (2θ ≤ 53.516°), and 157 parameters. CCDC 1485955. Crystallographic Details for 2b. The crystal data of 2b were collected on a Bruker D8 Quest diffractometer with a CMOS area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using an intrinsic phasing method (ShelXT), refined with the ShelXLprogram,25 and expanded using Fourier techniques. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions.

■

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.6b00495.

■

Experimental and computational procedures (PDF) Crystallographic data (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail for H.B.: [email protected]. F

DOI: 10.1021/acs.organomet.6b00495 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Notes

(16) (a) Einstein, F. W. B.; Pomeroy, R. K.; Rushman, P.; Willis, A. C. J. Chem. Soc., Chem. Commun. 1983, 854−855. (b) Fleming, M. M.; Pomeroy, R. K.; Rushman, P. J. Organomet. Chem. 1984, 273, C33− C38. (c) Einstein, F. W. B.; Jennings, M. C.; Krentz, R.; Pomeroy, R. K.; Rushman, P.; Willis, A. C. Inorg. Chem. 1987, 26, 1341−1344. (d) Davis, H. B.; Einstein, F. W. B.; Glavina, P. G.; Jones, T.; Pomeroy, R. K.; Rushman, P. Organometallics 1989, 8, 1030−1039. (e) Batchelor, R. J.; Davis, H. B.; Einstein, F. W. B.; Pomeroy, R. K. J. Am. Chem. Soc. 1990, 112, 2036−2037. (f) Shipley, J. A.; Batchelor, R. J.; Einstein, F. W. B.; Pomeroy, R. K. Organometallics 1991, 10, 3620−3629. (g) Batchelor, R. J.; Einstein, F. W. B.; Pomeroy, R. K.; Shipley, J. A. Inorg. Chem. 1992, 31, 3155−3157. (h) Jiang, F.; Male, J. L.; Biradha, K.; Leong, W. K.; Pomeroy, R. K.; Zaworotko, M. J. Organometallics 1998, 17, 5810−5819. (i) Jiang, F.; Jenkins, H. A.; Biradha, K.; Davis, H. B.; Pomeroy, R. K.; Zaworotko, M. J. Organometallics 2000, 19, 5049−5062. (17) (a) Le Bozec, H.; Dixneuf, P. H.; Adams, R. D. Organometallics 1984, 3, 1919−1921. (b) Coco, S.; Espinet, P.; Mayor, F.; Solans, X. J. Chem. Soc., Dalton Trans. 1991, 2503−2509. (c) Song, L.; Trogler, W. C. Angew. Chem., Int. Ed. Engl. 1992, 31, 770−772. (d) Bodensieck, U.; Braunstein, P.; Knorr, M.; Strampfer, M.; Bénard, M.; Strohmann, C. Angew. Chem., Int. Ed. Engl. 1997, 36, 2758−2761. (e) Song, H.-B.; Wang, Q.-M.; Zhang, Z.-Z.; Mak, T. C. W. J. Organomet. Chem. 2000, 605, 15−21. (f) Song, H.-B.; Zhang, Z.-Z.; Mak, T. C. W. Inorg. Chem. 2001, 40, 5928−5933. (g) Song, H.-B.; Zhang, Z.-Z.; Mak, T. C. W. New J. Chem. 2002, 26, 113−119. (18) Martin, L. R.; Einstein, F. W. B.; Pomeroy, R. K. Inorg. Chem. 1985, 24, 2777−2785. (19) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.; Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans. 2008, 2832−2838. (20) (a) Moore, E. J.; Sullivan, J. M.; Norton, J. R. J. Am. Chem. Soc. 1986, 108, 2257−2263. (b) Jordan, R. F.; Norton, J. R. J. Am. Chem. Soc. 1982, 104, 1255−1263. (21) (a) Angelici, R. J. Acc. Chem. Res. 1995, 28, 51−60. (b) Sowa, J. R., Jr.; Zanotti, V.; Facchin, G.; Angelici, R. J. J. Am. Chem. Soc. 1991, 113, 9185−9192. (c) Sowa, J. R., Jr.; Zanotti, V.; Angelici, R. J. Inorg. Chem. 1993, 32, 848−853. (d) Rottink, M. K.; Angelici, R. J. J. Am. Chem. Soc. 1993, 115, 7267−7274. (22) Luetkens, M. L.; Sattelberger, A. P.; Murray, H. H.; Basil, J. D.; Fackler, J. P.; Jones, R. A.; Heaton, D. E. Inorg. Synth. 1990, 28, 305− 310. (23) Bantreil, X.; Nolan, S. P. Nat. Protoc. 2011, 6, 69−77. (24) Bellachioma, G.; Cardaci, G.; Macchioni, A.; Zanazzi, P. Inorg. Chem. 1993, 32, 547−553. (25) Sheldrick, G. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122.

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors gratefully acknowledge the Deutsche Forschungsgemeinschaft for financial support of this work.

■

REFERENCES

(1) (a) Vaska, L. Acc. Chem. Res. 1968, 1, 335−344. (b) Collman, J. P.; Roper, W. R. Adv. Organomet. Chem. 1969, 7, 53−94. (c) Shriver, D. F. Acc. Chem. Res. 1970, 3, 231−238. (d) Werner, H. Pure Appl. Chem. 1982, 54, 177−188. (e) Werner, H. Angew. Chem., Int. Ed. Engl. 1983, 22, 927−949. (2) Coffey, C. E.; Lewis, J.; Nyholm, R. S. J. Chem. Soc. 1964, 0, 1741−1749. (3) Nowell, I. N.; Russell, D. R. Chem. Commun. 1967, 0, 817. (4) (a) Hill, A. F.; Owen, G. R.; White, A. J. P.; Williams, D. J. Angew. Chem., Int. Ed. 1999, 38, 2759−2761. (b) Foreman, M. R. St.-J.; Hill, A. F.; White, A. J. P.; Williams, D. J. Organometallics 2004, 23, 913− 916. (5) (a) Kuzu, I.; Krummenacher, I.; Meyer, J.; Armbruster, F.; Breher, F. Dalton Trans. 2008, 5836−5865. (b) Braunschweig, H.; Dewhurst, R. D.; Schneider, A. Chem. Rev. 2010, 110, 3924−3957. (c) Braunschweig, H.; Dewhurst, R. D. Dalton Trans. 2011, 40, 549− 558. (6) Selected examples of supported M→E complexes from 2015 to 2016: (a) Chapman, A. M.; Flynn, S. R.; Wass, D. F. Inorg. Chem. 2016, 55, 1017−1021. (b) Yang, H.; Gabbaï, F. P. J. Am. Chem. Soc. 2015, 137, 13425−13432. (c) Jones, S. J.; Gabbaï, F. P. Chem. Lett. 2016, 45, 376−384. (d) Devillard, M.; Declerq, R.; Nicolas, E.; Ehlers, A. W.; Backs, J.; Saffon-Merceron, N.; Bouhadir, G.; Slootweg, J. C.; Uhl, W.; Bourissou, D. J. Am. Chem. Soc. 2016, 138, 4917−4926. (e) Anderson, J. S.; Cutsail, G. E., III; Rittle, J.; Connor, B. A.; Gunderson, W. A.; Zhang, L.; Hoffman, B. M.; Peters, J. C. J. Am. Chem. Soc. 2015, 137, 7803−7809. (f) Del Castillo, T. J.; Thompson, N. B.; Peters, J. C. J. Am. Chem. Soc. 2016, 138, 5341−5350. (7) Bauer, J.; Braunschweig, H.; Dewhurst, R. D. Chem. Rev. 2012, 112, 4329−4346. (8) (a) Bauer, J.; Braunschweig, H.; Dewhurst, R. D.; Radacki, K. Chem. - Eur. J. 2013, 19, 8797−8805. (b) Hupp, F.; Ma, M.; Kroll, F.; Jimenez-Halla, J. O. C.; Dewhurst, R. D.; Radacki, K.; Stasch, A.; Jones, C.; Braunschweig, H. Chem. - Eur. J. 2014, 20, 16888−16898. (c) Braunschweig, H.; Dewhurst, R. D.; Hupp, F.; Schneider, C. Chem. Commun. 2014, 50, 15685−15688. (d) Braunschweig, H.; Dewhurst, R. D.; Hupp, F.; Kaufmann, C.; Phukan, A. K.; Schneider, C.; Ye, Q. Chem. Sci. 2014, 5, 4099−4104. (e) Braunschweig, H.; Celik, M. A.; Dewhurst, R. D.; Heid, M.; Hupp, F.; Sen, S. S. Chem. Sci. 2015, 6, 425−435. (f) Braunschweig, H.; Dewhurst, R. D.; Hupp, F.; Wolf, J. Chem. - Eur. J. 2015, 21, 1860−1862. (g) Braunschweig, H.; Brunecker, C.; Dewhurst, R. D.; Schneider, C.; Wennemann, B. Chem. - Eur. J. 2015, 21, 19195−19201. (h) Braunschweig, H.; Dewhurst, R. D.; Schneider, C. Organometallics 2016, 35, 1002−1007. (9) Ma, M.; Sidiropoulos, A.; Ralte, L.; Stasch, A.; Jones, C. Chem. Commun. 2013, 49, 48−50. (10) Malinowski, P. J.; Krossing, I. Angew. Chem., Int. Ed. 2014, 53, 13460−13462. (11) Swarnakar, A. K.; Ferguson, M. J.; McDonald, R.; Rivard, E. Dalton Trans. 2016, 45, 6071−6078. (12) Itazaki, M.; Ito, M.; Nakashima, S.; Nakazawa, H. Dalton Trans. 2016, 45, 1327−1330. (13) Barnett, B. R.; Moore, C. E.; Chandrasekaran, P.; Sproules, S.; Rheingold, A. L.; DeBeer, S.; Figueroa, J. S. Chem. Sci. 2015, 6, 7169− 7178. (14) Blake, M. P.; Kaltsoyannis, N.; Mountford, P. J. Am. Chem. Soc. 2015, 137, 12352−12368. (15) Omoto, K.; Tashiro, S.; Shionoya, M. Z. Anorg. Allg. Chem. 2015, 641, 2056−2059. G

DOI: 10.1021/acs.organomet.6b00495 Organometallics XXXX, XXX, XXX−XXX