Letter pubs.acs.org/acscatalysis
Catalytic Dehydrogenation of Dimethylamine Borane by Highly Active Thorium and Uranium Metallocene Complexes Karla A. Erickson and Jaqueline L. Kiplinger* Chemistry Division, Mail Stop J514, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United States S Supporting Information *
ABSTRACT: The thorium and uranium complexes (C5Me5)2AnMe2, [(C5Me5)2An(H)(μ-H)]2 (An = Th, U) and [(C5Me5)2U(H)]2 dehydrogenate dimethylamine borane (Me2NH·BH3) at room temperature. Upon mild heating at 45 °C, turnover frequencies (TOFs) of 400 h−1 are obtained, which is comparable to some of the fastest Me2NH·BH3 dehydrogenation catalysts known in the literature. A β-hydride elimination mechanism for dehydrogenation is proposed because of the observation of Me2NBH2, Me2NBMe2, and Me2NBHMe in the 11B NMR spectra of catalytic and stoichiometric reactions. The similar catalytic metrics between the actinide dimethyl and hydride complexes with Me2NH·BH3 indicate that the actinide hydride complexes are the active catalysts in this chemistry. KEYWORDS: actinide catalysis, thorium and uranium metallocene complexes, pentamethylcyclopentadienyl ligand, dimethylamine borane, dehydrogenation, dehydrocoupling
T
he study of amine borane (RR′HN·BH3) dehydrogenation is a rich and comprehensive field that encompasses investigations using transition-metal,1−5 main-group metal,6,7 and lanthanide8−13 catalysts. However, there has been one glaring omission: analogous chemistry with the actinides has been ignored. Barring studies of tris(pyrazolyl)borate-supported thorium and uranium complexes,14−16 less than a handful of reports exist where interactions between organoactinides and B−Ncontaining molecules have been examined. For example, the Girolami group studied actinide amidoboronate (H3BNMe2BH3−) complexes, finding them to be highly volatile17 and, until recently,18,19 exhibiting some of the highest Werner coordination numbers known.20−22 In addition, Braunschweig and co-workers reacted (C5Me5)2UMe2 and (1,2,4-tBu3-C5H2)2UMe2 with the amino borane (Me3Si)2N BH2 to prepare (C5Me5)2U[H3BN(SiMe3)2]2 and (1,2,4-tBu3C5H2)2U[H3BN(SiMe3)2], respectively.23 We have been interested in developing routes that avoid the use of H2 gas to thorium(IV), uranium(IV), and uranium(III) hydrides to expand and better understand their chemistry.24,25 During our studies, we discovered that the actinide dimethyl complexes (C5Me5)2AnMe2 (An = Th (1), U (2)) and hydride complexes, [(C5Me5)2An(H)(μ-H)]2 (An = Th (3), U (4)) and [(C 5 Me 5 ) 2 UH] 2 (5; see Figure 1), catalyze the dehydrogenation of dimethylamine borane (Me2NH·BH3, 6) with metrics comparable to those previously reported for highly active Rh and Ru catalysts. Given the unique role that actinides and their hydrides play in the energy and security sectors throughout the DOE complex, these results emphasize that the chemistry between © 2017 American Chemical Society
Figure 1. Actinide complexes selected for the catalytic dehydrogenation of dimethylamine borane.
main-group hydrides and actinides is under-studied, but important to comprehend.26−33 As shown in Scheme 1, reaction of the known thorium and uranium dimethyl complexes, (C5Me5)2AnMe2 (An = Th (1), Scheme 1. Dimethylamine Borane Dehydrogenation with Actinide Complexes 1−5
Received: March 24, 2017 Revised: May 17, 2017 Published: May 19, 2017 4276
DOI: 10.1021/acscatal.7b00967 ACS Catal. 2017, 7, 4276−4280
Letter
ACS Catalysis U (2)), and hydride complexes, [(C5Me5)2An(H)(μ-H)]2 (An = Th (3), U (4)) and [(C5Me5)2UH]2 (5), with dimethylamine borane (Me2NH·BH3, 6) in benzene-d6 at room temperature resulted in vigorous H2 gas evolution and formed a mixture of the cyclic borazane [Me2N·BH2]2 (6a), linear borazane Me2NH·BH2−NMe2·BH3 (6b), amino borane Me2NBH2 (6c), diamino borane (Me2N)2BH (6d), amino borane Me2NBMe2 (6e), and amino borane Me2NBHMe (6f) under a variety of stoichiometric and catalyst loadings. To assess the ability of 1−5 to catalytically liberate H2 from Me2NH·BH3 (6), nuclear magnetic resonance (NMR) studies were performed. The reaction of 6 with 5 mol % 1 or 2 in benzene-d6 was monitored by 1H and 11B NMR spectroscopy, which indicated that Me2NH·BH3 was completely converted to the dehydrogenated products 6a−6d after 2−3 h at room temperature (Table 1). The catalyst loadings for complexes 1−
Table 2. Product Distribution of 6a−6d as a Function of Catalyst Loadinga catalyst
loading (mol %)
6a (%)
6b (%)
6c (%)
6d (%)
1 1 1b 1 2 2b 2 3 4 5
1 0.5 0.5 0.2 1 0.5 0.2 2 2 2
94 96 99 54 98 99 75 98 93 92
2.8 2.9 0 46 0 0 25 0 3.7 5.5
0 0.9 0 0 0 0 0 0 0.9 0.92
2.8 0.1 (trace) 0.9 0 2 1 0 2 2.4 1.81
a
Reaction in benzene-d6 at room temperature in an unsealed scintillation vial; product distribution determined by integration of 11 B NMR spectra. bReaction heated to 45 °C.
Table 1. Dimethylamine Borane Dehydrogenation by Actinide Catalysts 1−5a catalyst
loading (mol %)
turnover number, TON
turnover frequency, TOF (h−1)
1 1 1 1 1b 1 2 2 2 2 2b 3 4 5
5 2 1 0.5 0.5 0.2 5 2 1 0.2 0.5 2 2 2
20 50 99 198 200 421 21 52 106 497 193 66 54 48
10 25 198 66 400 70 10 26 212 83 386 33 27 24
a
Reaction in benzene-d6 at room temperature in an unsealed scintillation vial; TON and TOF are determined by integration of 11 B NMR spectra. bReaction heated to 45 °C.
Figure 2. Comparison of highly active dimethylamine borane dehydrogenation catalysts.
5 were reduced and resulted in high turnover numbers (TONs) and turnover frequencies (TOFs, Table 1). Room-temperature reactions achieved TOFs of ∼200 h−1; however, mild heating at 45 °C resulted in TOFs of ∼380 h−1. As summarized in Table 1, no significant differences in catalytic reactivity were observed between (1) thorium versus uranium catalysts, (2) dialkyl versus hydride catalysts, or (3) uranium(III) versus uranium(IV) hydride catalysts. Table 2 summarizes the product distribution that is observed under catalytic conditions. In all reactions, the cyclic borazane [Me2N·BH2]2 (6a, 11B NMR δ: 5.4 (t))34 is the major product, as determined by 11B NMR spectroscopy. The linear borazane Me2NH·BH2−NMe2·BH3 (6b, 11B NMR δ: 2.0 (t), −13.2 (q))35 is also observed in significant quantities at lower loadings (0.2 mol % and 0.5 mol %) due to concentration effects.36 In addition, the amino borane Me2NBH2, (6c, 11B NMR δ: 38.1 (t))37 and the diamino borane (Me2N)2BH (6d, 11B NMR δ: 29.7 (d)),36 are observed at higher catalyst loadings and never in quantities greater than ∼3%. Figure 2 shows the catalytic metrics for the most reactive Me2NH·BH3 (6) dehydrogenation catalysts that have been reported in the literature. At ambient temperatures, (C5Me5)2AnMe2 (An = Th (1), U (2)) is most comparable
to [(η6-C6H6)Ru(2,6-Me2-C6H3NCMe)2CH][OTf] (7)38 and shows better catalytic metrics than [Rh(1,5-cod)(μ-Cl)]2 (8).34 However, the rare-earth-metal complex, (C5H5BMe)2Y[CH(SiMe3)2] (9),39 exhibits higher TOFs, which may be attributed to the electron-withdrawing 1-methylboratabenzene ligand, since the electron-donating 1-triethylamineboratabenzene congener exhibited modest TOFs (9.4 h−1). Additionally, two electrophilic Rh catalysts, [(η6-C6H5F)Rh2 (η -(P,P)-PPh2(CH2)3PPh2] (10)40 and (Xantphos)Rh(H2B(NMe3)(CH2)2(tBu) (11)41 exhibit TOFs similar to 9, indicating that further improvements in catalytic dehydrogenation may be accessible through electron-withdrawing ligands and electrophilic metal centers. Significant efforts have gone toward elucidating the mechanisms of Me2NH·BH3 dehydrogenation by complex metal hydrides.3,37,42−54 This vast body of work has shown that the formation of Me2NBH2 (6c) results from either βhydride elimination from an intermediate σ-N-bound amidoborane complex ([LnM]−NMe2BH3) or σ-B-bound aminoboryl complex ([LnM]−BH2NHMe2). The thus formed Me2NBH2 (6c) is reactive and produces the cyclic borazane [Me2NBH2]2 (6a) and linear borazane Me2NH·BH2−NMe2·BH3 (6b).5 4277
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Scheme 2. Proposed Mechanisms for the Formation of Me2NBMe2 (6e, Left), Me2NBHMe (6f, Middle), and the Catalytic Dehydrogenation of Dimethylamine Borane (6) with Actinide Complexes 1−5 (Right)
Although β-hydride elimination from actinide complexes is relatively rare,55,56 observation of Me2NBH2 (6c) is fully consistent with β-hydride elimination and indicates that the catalytic species are the hydride complexes (3−5) and not the alkyl complexes (1 and 2). To confirm this, we investigated the stoichiometric reactions of (C5Me5)2AnMe2 (An = Th (1), U (2)) with Me2NH·BH3 (6). Because uranium(IV) is a paramagnetic center, the uranium-containing compounds feature broadly spaced and sharp resonances, which conveniently do not overlap with those associated with dehydrogenation products in the 1H NMR spectra. As such, we primarily used the paramagnetic uranium and not the diamagnetic thorium compound for the following studies. The reaction of (C5Me5)2UMe2 (2) with 1 equiv of Me2NH· BH3 (6) in benzene-d6 at room temperature resulted in vigorous gas evolution and formation of the σ-B-bound amino boryl hydride complex (C5Me5)2U(H)(BMe2·NHMe2) (13), which was assigned by three singlets in the 1H NMR spectrum at δ 5.11 (30 H), 5.21 (6 H) and −19.00 (6 H), corresponding to the C5Me5, NMe2, and BMe2 resonances (Scheme 2, left panel). Initial conversion of 2 to 13 is proposed to occur by ligand exchange of two hydrides on Me2NH·BH3 (6) with both methyl groups at the uranium metal center, forming Me2NH· BMe2H (12, not observed) and [(C5Me5)2U(H)(μ-H)]2 (4). Although rare, there is precedent for alkyl transfer from electrophilic zirconium and uranium metal centers to boron to generate the corresponding complex metal hydrides.5,57 The thus-formed Me2NH·BMe2H reacts with 4 to give the σ-Bbound aminoboryl hydride complex (C5Me5)2U(H)(BMe2· NHMe2) (13), which undergoes β-hydride elimination to afford Me2NBMe2 (6e, observed, 11B NMR: δ 44.8 (s))58 and the active catalyst 4. Upon the addition of 2 equiv of Me2NH·BH3 (6) to (C5Me5)2UMe2 (2), new resonances ascribable to the σ-Bbound bis(aminoboryl) complex (C5Me5)2U(BHMe·NHMe2)2 (16) are found in the 1H NMR spectrum at δ 6.74 (s, 30 H, C5Me5), 6.59 (s, 12 H, NHMe2), and −16.08 (s, 6H, BHMe). β-
hydride elimination from 16 eliminates Me2NBHMe (6f, observed, 11B NMR: δ 41.8 (d)).58 The amino borane 6f is also observed in analogous reactions with the thorium dimethyl complex, (C5Me5)2ThMe2 (1), and 2 equiv of 6. Therefore, we propose that both the thorium(IV) and uranium(IV) compounds undergo a redox-neutral mechanism, as detailed in the middle panel of Scheme 2. These results were further corroborated through deuteriumlabeling studies where (C5Me5)2An(CD3)2 (An = Th (1-d6), U (2-d6)) were reacted under similar conditions with Me2NH· BH3 (6). By 2H NMR spectroscopy, only resonances corresponding to amino boranes and no resonances for methane isotopomers were observed. This further confirms that methyl group-transfer from the thorium and uranium complexes to boron is operative rather than liberation of methane. The combined data clearly show that the actinide hydride complexes are the active catalysts. This proposed mechanism allows for entry into the complex metal hydride-catalyzed dehydrogenation of Me2NH·BH3 (6), which is summarized in the right panel of Scheme 2. The thorium(IV) hydride complex (3) has been shown to be stable for hours in a toluene solution at 80 °C; however, the uranium derivative [(C5Me5)2U(H)(μ-H)]2 (4) reversibly loses H2 at ambient temperature to form the trivalent uranium hydride complex [(C5Me5)2UH]2 (5), according to eq 1.59
Since both [(C5Me5)2U(H)(μ-H)]2 (4) and [(C5Me5)2UH]2 (5) are shown to act similarly in the catalytic dehydrogenation of Me2NH·BH3 (6, Table 1), it is possible for both the uranium(III) and uranium(IV) hydrides to be present in the catalytic reaction. Both are included in our proposed catalytic cycle, even though the sharp NMR signals observed in the 4278
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(11) Cui, P.; Spaniol, T. P.; Maron, L.; Okuda, J. Chem.Eur. J. 2013, 19, 13437−13444. (12) Rad’kov, V.; Dorcet, V.; Carpentier, J.-F.; Trifonov, A.; Kirillov, E. Organometallics 2013, 32, 1517−1527. (13) Hill, M. S.; Kociok-Kohn, G.; Robinson, T. P. Chem. Commun. 2010, 46, 7587−7589. (14) Paulo, A.; Correia, J. D. G.; Campello, M. P. C.; Santos, I. Polyhedron 2004, 23, 331−360. (15) Sessler, J. L.; Melfi, P. J.; Pantos, G. D. Coord. Chem. Rev. 2006, 250, 816−843. (16) Liddle, S. T. Angew. Chem., Int. Ed. 2015, 54, 8604−8641. (17) Vlaisavljevich, B.; Miró, P.; Koballa, D.; Todorova, T. K.; Daly, S. R.; Girolami, G. S.; Cramer, C. J.; Gagliardi, L. J. Phys. Chem. C 2012, 116, 23194−23200. (18) Pollak, D.; Goddard, R.; Pörschke, K.-R. J. Am. Chem. Soc. 2016, 138, 9444−9451. (19) Popov, I. A.; Jian, T.; Lopez, G. V.; Boldyrev, A. I.; Wang, L.-S. Nat. Commun. 2015, 6, 8654. (20) Daly, S. R.; Girolami, G. S. Inorg. Chem. 2010, 49, 5157−5166. (21) Daly, S. R.; Piccoli, P. M. B.; Schultz, A. J.; Todorova, T. K.; Gagliardi, L.; Girolami, G. S. Angew. Chem., Int. Ed. 2010, 49, 3379− 3381. (22) Daly, S. R.; Girolami, G. S. Chem. Commun. 2010, 46, 407−408. (23) Braunschweig, H.; Gackstatter, A.; Kupfer, T.; Radacki, K.; Franke, S.; Meyer, K.; Fucke, K.; Lemée-Cailleau, M. H. Inorg. Chem. 2015, 54, 8022−8028. (24) Pagano, J. K.; Dorhout, J. M.; Czerwinski, K. R.; Morris, D. E.; Scott, B. L.; Waterman, R.; Kiplinger, J. L. Organometallics 2016, 35, 617−620. (25) Pagano, J. K.; Dorhout, J. M.; Waterman, R.; Czerwinski, K. R.; Kiplinger, J. L. Chem. Commun. 2015, 51, 17379−17381. (26) Fox, A. R.; Bart, S. C.; Meyer, K.; Cummins, C. C. Nature 2008, 455, 341−349. (27) Barnea, E.; Eisen, M. S. Coord. Chem. Rev. 2006, 250, 855−899. (28) Andrea, T.; Eisen, M. S. Chem. Soc. Rev. 2008, 37, 550−567. (29) Eisen, M. In C−X Bond Formation; Vigalok, A., Ed.; Springer: Berlin, Heidelberg, 2010; Vol. 31, pp 157−184. (30) Baker, R. J. Chem. - Eur. J. 2012, 18, 16258−16271. (31) Lam, O. P.; Meyer, K. Polyhedron 2012, 32, 1−9. (32) Turner, Z. Inorganics 2015, 3, 597. (33) Karmel, I.; Batrice, R.; Eisen, M. Inorganics 2015, 3, 392. (34) Jaska, C. A.; Temple, K.; Lough, A. J.; Manners, I. J. Am. Chem. Soc. 2003, 125, 9424−9434. (35) Nöth, H.; Thomas, S. Eur. J. Inorg. Chem. 1999, 1999, 1373− 1379. (36) Friedrich, A.; Drees, M.; Schneider, S. Chem.Eur. J. 2009, 15, 10339−10342. (37) Vance, J. R.; Schäfer, A.; Robertson, A. P. M.; Lee, K.; Turner, J.; Whittell, G. R.; Manners, I. J. Am. Chem. Soc. 2014, 136, 3048−3064. (38) Schreiber, D. F.; O’Connor, C.; Grave, C.; Ortin, Y.; MüllerBunz, H.; Phillips, A. D. ACS Catal. 2012, 2, 2505−2511. (39) Lu, E.; Yuan, Y.; Chen, Y.; Xia, W. ACS Catal. 2013, 3, 521− 524. (40) Dallanegra, R.; Robertson, A. P. M.; Chaplin, A. B.; Manners, I.; Weller, A. S. Chem. Commun. 2011, 47, 3763−3765. (41) Johnson, H. C.; Leitao, E. M.; Whittell, G. R.; Manners, I.; Lloyd-Jones, G. C.; Weller, A. S. J. Am. Chem. Soc. 2014, 136, 9078− 9093. (42) Stevens, C. J.; Dallanegra, R.; Chaplin, A. B.; Weller, A. S.; Macgregor, S. A.; Ward, B.; McKay, D.; Alcaraz, G.; Sabo-Etienne, S. Chem. - Eur. J. 2011, 17, 3011−3020. (43) Vance, J. R.; Robertson, A. P. M.; Lee, K.; Manners, I. Chem. Eur. J. 2011, 17, 4099−4103. (44) Bénac-Lestrille, G.; Helmstedt, U.; Vendier, L.; Alcaraz, G.; Clot, E.; Sabo-Etienne, S. Inorg. Chem. 2011, 50, 11039−11045. (45) Beweries, T.; Thomas, J.; Klahn, M.; Schulz, A.; Heller, D.; Rosenthal, U. ChemCatChem 2011, 3, 1865−1868. (46) Beweries, T.; Hansen, S.; Kessler, M.; Klahn, M.; Rosenthal, U. Dalton Trans. 2011, 40, 7689−7692.
stoichiometric reactions suggest that the uranium(IV) pathway is operative. In summary, the classic organoactinide complexes (C5Me5)2AnMe2 (An = Th (1), U (2)), [(C5Me5)2An(H)(μH)]2 (An = Th (3), U (4)), and [(C5Me5)2UH]2 (5) all rapidly dehydrogenate Me2NH·BH3 (6) under conditions comparable to some of the fastest catalysts known in the literature. We conclude, through product analysis of stoichiometric reactions and deuterium labeling studies, that methyl-group transfer from the actinide metal center to 6 allows for the activation of precatalysts 1 and 2. Furthermore, this work shows that the actinide hydride complexes 3−5 are the active catalytic species and the catalytic cycle proceeds through a β-hydride elimination mechanism. Our research on the chemistry between actinides and main-group hydrides is ongoing and will be reported in due course.
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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/acscatal.7b00967. General procedure of NMR experiments and 11B NMR spectra for catalytic reactions (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. ORCID
Jaqueline L. Kiplinger: 0000-0003-0512-7062 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS For financial support of this work, we acknowledge the Los Alamos National Laboratory G. T. Seaborg Institute for Transactinium Science and the LANL LDRD Program (PD Fellowship to K.A.E.). Los Alamos National Laboratory is operated by Los Alamos National Security, LLC, for the National Nuclear Security Administration of U.S. Department of Energy (Contract No. DE-AC52-06NA25396).
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REFERENCES
(1) Rossin, A.; Peruzzini, M. Chem. Rev. 2016, 116, 8848−8872. (2) Staubitz, A.; Robertson, A. P. M.; Manners, I. Chem. Rev. 2010, 110, 4079−4124. (3) Staubitz, A.; Robertson, A. P. M.; Sloan, M. E.; Manners, I. Chem. Rev. 2010, 110, 4023−4078. (4) Stubbs, N. E.; Robertson, A. P. M.; Leitao, E. M.; Manners, I. J. Organomet. Chem. 2013, 730, 84−89. (5) Johnson, H. C.; Hooper, T. N.; Weller, A. S. In Synthesis and Application of Organoboron Compounds; Fernández, E., Whiting, A., Eds.; Springer International Publishing: Cham, Switzerland, 2015; pp 153−220. (6) Melen, R. L. Chem. Soc. Rev. 2016, 45, 775−788. (7) Crimmin, M. R.; Hill, M. S. In Alkaline-Earth Metal Compounds: Oddities and Applications; Harder, S., Ed.; Springer: Berlin, Heidelberg, 2013; pp 191−241. (8) Li, J.; Gao, D.; Hu, H.; Cui, C. New J. Chem. 2015, 39, 7567− 7570. (9) Daly, S. R.; Kim, D. Y.; Yang, Y.; Abelson, J. R.; Girolami, G. S. J. Am. Chem. Soc. 2010, 132, 2106−2107. (10) Daly, S. R.; Girolami, G. S. Inorg. Chem. 2010, 49, 4578−4585. 4279
DOI: 10.1021/acscatal.7b00967 ACS Catal. 2017, 7, 4276−4280
Letter
ACS Catalysis (47) Sewell, L. J.; Lloyd-Jones, G. C.; Weller, A. S. J. Am. Chem. Soc. 2012, 134, 3598−3610. (48) Tang, C. Y.; Phillips, N.; Bates, J. I.; Thompson, A. L.; Gutmann, M. J.; Aldridge, S. Chem. Commun. 2012, 48, 8096−8098. (49) Helten, H.; Dutta, B.; Vance, J. R.; Sloan, M. E.; Haddow, M. F.; Sproules, S.; Collison, D.; Whittell, G. R.; Lloyd-Jones, G. C.; Manners, I. Angew. Chem., Int. Ed. 2013, 52, 437−440. (50) Sewell, L. J.; Huertos, M. A.; Dickinson, M. E.; Weller, A. S.; Lloyd-Jones, G. C. Inorg. Chem. 2013, 52, 4509−4516. (51) Less, R. J.; Simmonds, H. R.; Dane, S. B. J.; Wright, D. S. Dalton Trans. 2013, 42, 6337−6343. (52) Roselló-Merino, M.; López-Serrano, J.; Conejero, S. J. Am. Chem. Soc. 2013, 135, 10910−10913. (53) Butera, V.; Russo, N.; Sicilia, E. Chem.Eur. J. 2014, 20, 5967− 5976. (54) Klahn, M.; Hollmann, D.; Spannenberg, A.; Bruckner, A.; Beweries, T. Dalton Trans. 2015, 44, 12103−12111. (55) Bruno, J. W.; Kalina, D. G.; Mintz, E. A.; Marks, T. J. J. Am. Chem. Soc. 1982, 104, 1860−1869. (56) Arnold, P. L.; McMullon, M. W.; Rieb, J.; Kühn, F. E. Angew. Chem., Int. Ed. 2015, 54, 82−100. (57) Miyazaki, T.; Tanabe, Y.; Yuki, M.; Miyake, Y.; Nishibayashi, Y. Organometallics 2011, 30, 2394−2404. (58) Stubbs, N. E.; Schäfer, A.; Robertson, A. P. M.; Leitao, E. M.; Jurca, T.; Sparkes, H. A.; Woodall, C. H.; Haddow, M. F.; Manners, I. Inorg. Chem. 2015, 54, 10878−10889. (59) Fagan, P. G.; Manriquez, J. M.; Maatta, E. A.; Seyam, A. M.; Marks, T. J. J. Am. Chem. Soc. 1981, 103, 6650−6667.
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