Editorial pubs.acs.org/IC
Metal−Metal Bonds: From Fundamentals to Applications
T
he year 2017 marks the 10th anniversary of the passing of Prof. F. Albert Cotton, who described the first metal−metal multiple bonds in 1964.1 Cotton’s contributions to our understanding of metal−metal bonds were undeniably monumental, but nobody could claim that this field has died with him. Quite the contrarythe past 10 years have seen a renewed interest in metal−metal bonds, especially from a growing cadre of younger scientists in the early stages of their careers. Bonds between metals continue to expand beyond quadruple to bond orders of 5 or 6.2 Synthetic chemists have applied their creativity to design compounds featuring new subclasses of metal−metal bonds that have heretofore not been seen, be they bonds among the transition metals, main-group elements, or even the long-overlooked f-block elements. From experimental to spectroscopic to computational, the development of new tools to study the electronic structure of metal−metal-bonded compounds continues to enlighten our understanding of bonding. This evolving perspective of metal−metal bonding allows for the use of metal−metalbonded compounds in important applications: as structural subunits of metal−organic frameworks, molecular-scale conductors, photosensitizers, and catalysts. This virtual issue http://pubs.acs.org/page/vi/metal-metal-bonds highlights recent publications from Inorganic Chemistry, Journal of the American Chemical Society, and Organometallics, among others, that survey the breadth of current activity that involves metal− metal bonds. We hope that our readers will be inspired by the articles in this virtual issue and, despite the specialized focus on metal−metal bonds, learn new lessons of relevance, interest, and importance to the larger chemistry community.
Figure 1. Phosphorus/nitrogen or oxygen ligands for supporting metal−metal bonds developed by Lu, Thomas, and Arnold.
In the first highlighted paper of this current issue, the Thomas group capitalizes on the mixed-donor-ligand strategy to support heterobimetallic complexes featuring Ti−M and V−M cores, where M = Fe, Co, Ni, and Cu.7 In these heterobimetallic complexes, the covalent metal−metal bonds make it unwieldy to assign separate oxidation states to the metals, and Thomas has promoted the use of [MM′]n notation, not unlike Enemark−Feldham notation for metal nitrosyls,8 in which n is the sum of the d electrons available from M and M′. The Ti−M and V−M series span an array of [MM′]n compounds with n ranging from 8 to 12, covering a range of metal−metal bond orders from 3 to less than 1. While the study of metal−metal bonds has historically been limited to the transition elements, uranium is an element that has fascinated many researchers. In 1984, Cotton remarked that the outlook for compounds with U−U bonds was “rather dim”,9 but recent work from the group of Arnold gives us glimmers of hope. In the current virtual issue, the Arnold group describes a systematic series of complexes in which U(IV) is held in close proximity to a d10 group 10 metal, Ni, Pd, or Pt.10 These complexes feature short U−M distances, ranging from 2.53 to 2.71 Å, indicative of small but nonzero metal−metal bond orders. Another novel approach to making new bonds with uranium is that presented by Dehnen and co-workers, who use Zintl-type polyanionic clusters to encapsulate a U atom. For example, the [U@Bi12]3− cluster is an unusual odd-electron species in which the central U atom interacts with six Bi atoms at distances of 3.12−3.17 Å. While simple electron counting would suggest that U(III) is encapsulated by a closed-shell Bi126− ion, magnetic measurements and density functional theory calculations suggest instead that the U atom is trapped as U(IV) by an unusual open-shell Bi127− polyanion.11
■
NEW SYNTHETIC ARENAS FOR METAL−METAL BONDING Our issue begins with studies of new types of metal−metal bonds and their electronic structure. In 1844, French chemist M. Eugene Peligot prepared what he described as “petits cristaux rouges et transparents” upon the addition of potassium acetate to an aqueous solution of Cr(II).3 At the time, it was impossible for Peligot to know that he had prepared the first compound with a metal−metal multiple bond; it was not until 1970 that the structure of Cr2(OAc)4(OH2)2 was solved crystallographically and a short Cr−Cr distance of 2.36 Å was determined.4 Despite over 150 years of advances in the chemistry of multiply bonded dichromium compounds, compounds featuring multiple bonds between first-row transition metals other than chromium remained elusive until Cotton and Murillo succeeded in preparing the first compound with a VV bond.5 More recently, there has been an explosion of work on new metal−metal multiple bonds between first-row metals, mainly from the groups of Lu and Thomas, based on ligands designed to enforce 3-fold symmetry around a heterobimetallic M−M′ axis (see Figure 1). A major breakthrough was the preparation of the first trigonally symmetric heterobimetallic complex with a CrFe bond distance of 1.94 Å, supported by a chelating set of N- and P-donor atoms.6 © 2017 American Chemical Society
■
INCREASING DIMENSIONALITY: FROM CLUSTERS TO EXTENDED NETWORKS TO THE SOLID STATE Electronic structure has important consequences for the properties of metal−metal-bonded compounds. Electron delocalization via metal−metal bonding (i.e., the double-exchange mechanism12,13) can give rise to compounds whose ground states have a very large value of S when high-spin metal centers are used. These effects are observed in triangular triiron compounds described by the Betley group. One-electron reduction of an Fe36+ compound to the Fe35+ state results in a contraction of Fe−Fe bond distances from the 2.51−2.61 Å Published: July 17, 2017 7577
DOI: 10.1021/acs.inorgchem.7b01330 Inorg. Chem. 2017, 56, 7577−7581
Inorganic Chemistry
Editorial
range to 2.43−2.46 Å.14 Electron delocalization among the three high-spin Fe atoms results in an S = 11/2 ground state, which, when coupled with the axial anisotropy of the compound, results in single-molecule magnetic behavior with a blocking temperature of 1.5 K. Moving over from Fe to Mn and increasing the cluster size from 3 to 4, the Zdilla group describes a tetramanganese cubane-type cluster with bridging and terminal imido ligands. Although ligand-field theory predicts an S = 3/2 ground state for each Mn(IV) ion, the Mn416+ complex is diamagnetic because of delocalization of the Mn4 orbitals via Mn−Mn bonds of 2.54−2.56 Å.15 Besides cluster geometries, one-dimensional chain structures based on metal−metal bonds have been of significant interest since the days of Krogmann salts16 and oligomeric platinum blues.17 In this issue, Uemura and co-workers utilize one of the prototypical platinum blues, platinum(II) cis-diamminepivalamidate, as a unit that is linked to paramagnetic diruthenium tetraacetate. The reaction between Pt2 and Ru2 precursors yields a number of products, one of the most interesting being an extended chain compound with a heterometallic [−Ru− Ru−Pt−Pt−Pt−Pt−]n backbone.18 In another example of heterometallic chain compounds that contain platinum, Doerrer and co-workers report the preparation of a family of thiocarboxylate compounds in which the ligand S atom binds to Pt and the O atom is bridged to a first-row transition-metal atom. These metal−ligand interactions rely on hard−soft acid−base principles, and these principles are further put to use by combining Pt−Cr dimers with the thiocyanate ion to yield a polymeric chain with a [−Pt−Cr−N−C−S−]n backbone.19 Metal−metalbonded compounds can also be incorporated into threedimensional structures such as metal−organic frameworks.20 Miyasaka and co-workers present a family of such frameworks built on metal−metal-bonded diruthenium subunits.21 Depending on the nature of the ligand supporting the diruthenium dimers, the resulting materials are either porous and take up nitric oxide or remain nonporous. Moreover, the degree of NO uptake can be finely tuned by judiciously chosen mixtures (solid solutions) of the porous or nonporous precursors. The ultimate extension of metal−metal bonding to three dimensions occurs in solid-state materials. Intermetallics are a class of compounds made up entirely of metals, and therefore the electronic structures of these materials feature metal−metal bonds exclusively. Advances in this field are being made both on understanding the nature of bonding in these compounds and in the development of novel synthetic methods. Just as the 18-electron rule has pervaded our conceptions of bonding in organometallic chemistry, an 18 − n rule for intermetallic compounds has recently been developed by Yannello and Fredrickson that serves as a conceptual bridge between the materials and molecular realms.22 In this formalism, 18 − n valence electrons can be attributed to transition-metal centers making n metal−metal bonds, as illustrated in Figure 2. On the synthetic front, Hoch and co-workers describe their advances in the use of electrocrystallization to access novel intermetallic phases. Most commonly used with mercury to form intermetallic amalgams, Hoch and co-workers expand this technique to other intermetallics such as Li3Ga13Sn and CsIn12.23 MoS2 and WS2 are important compounds with applications as catalysts for hydrogen production.24 The most stable form of WS2 consists of trigonal-prismatic WS6 units linked together, but a second phase (called the ZT phase) is also known in which W−W bonds form in a zigzag array. Suenaga, Quek, Eda, and co-workers show that the ZT phase can be accessed locally
Figure 2. The 18 − n rule at work. (a) ScAl3 contains 12 valence electrons, and therefore each Sc atom makes six Sc−Sc bonds. (b) ZrAl3 contains 13 valence electrons, so each Zr atom makes five Zr−Zr bonds. (c) NbAl3 contains 14 valence electrons, and each Nb atom makes four Nb−Nb bonds. Reproduced with permission from ref 22. American Chemical Society 2015.
by irradiation with an electron beam. Ultimately, tetrameric W4 units are observed to form, and the ZT phase is structurally characterized using high-angle annular-dark-field scanning transmission electron microscopy, revealing W−W distances of 2.8 Å.25
■
METAL−METAL COOPERATIVITY IN ORGANOMETALLIC CATALYSIS The plasticity of metal−metal bonds and their attendant electronic structures may be advantageous in the arena of organometallic catalysis, where novel dinuclear variations of classic organometallic elementary reactions are being increasingly unveiled. A key challenge is to understand how to wield metal−metal cooperativity to benefit catalysis. We highlight eight works in the area of organometallic catalysis, where the metal−metal interaction is integral to catalyst function. The first set of papers describes homobimetallic catalysts for mediating organic reactions, where a common strategy is to maintain the integrity of the metal−metal bonding throughout catalysis. Dirhodium tetracarboxylates have been known since 1973 to catalyze the extrusion of dinitrogen from organic diazo compounds,26 yielding superelectrophilic “carbenoid” intermediates capable of a vast array of C−C bond formations. The nature of the reactive “carbenoid” species has been clarified over time by a number of key studies including a linear freeenergy study by Doyle and co-workers in 1984 implicating a rhodium carbene complex as the key intermediate.27 Such an intermediate has been examined computationally28 and finally was first observed and spectroscopically characterized in 2013.29 Fürstner and co-workers have recently unveiled the first crystal structures of this important intermediate, the dirhodium carbene complex.30 Critical to their success, the authors used a ternary mixture of solvents to crystallize these elusive species at low temperature. The set of structural data summarized in Figure 3 enable deeper insight into the stereoelectronic underpinnings of the catalyst’s selectivity. In the next two papers, researchers employ the redox-active naphthridine−diimine ligand to create two adjacent substrate binding sites at the dimetal unit. Bera and co-workers reported a RuRu paddlewheel catalyst for the dehydrogenation of primary alcohols to aldehydes and dihydrogen.31 In a key step, the diruthenium alkoxide intermediate was proposed to undergo 7578
DOI: 10.1021/acs.inorgchem.7b01330 Inorg. Chem. 2017, 56, 7577−7581
Inorganic Chemistry
Editorial
in the homobimetallic catalysts in that the metal−metal bond is cleaved during catalysis! Also, dihydrogen activation by the heterobimetallic complex is heterolytic, which is similar to the reactivity characteristic of frustrated Lewis pairs.37 Captain and co-workers have also shown cooperative heterolysis of dihydrogen using a Pt−Sn bimetallic.38 On the basis of spectroscopic evidence, the authors propose an intriguing three-center Pt−H−Sn μ-hydride product, which could also be thought of as a platinum σ complex of H−SnR3. Transientmetal−metalbonded species may also play a significant role in palladium crosscoupling catalysis, and such a notion has generated lively debate in recent years. In this area, Chen and co-workers uncovered a Pd−Cu bimetallic complex featuring a bridging sp2 C atom and a short Pd−Cu distance of 2.55 Å.39 The bond distance within the Pd−Cu bimetallic matches closely to the calculated transitionstate structure of the transmetalation step in the Sonogashira Pd/ Cu cross-coupling reaction (Figure 5). Hence, the formation of
Figure 3. Structure of a dirhodium carbene intermediate with relevant bond distances. Adapted with permission from ref 30. American Chemical Society 2016.
Figure 4. Dinuclear variations of classic organometallic reactions that utilize five-centered reactivity.
β-hydride elimination via a five-center transition state involving both Ru centers (Figure 4a). In recent years, Uyeda and co-workers have developed dinickel catalysts for a variety of reactions, including hydrosilylation of alkenes, alkynes, and CO substrates. The dinickel complex can bind secondary organosilanes, e.g., Ph2SiH2, to generate an interesting five-center intermediate that is somewhere between a double Si−H σ adduct and a double Si−H oxidative addition at both Ni centers (Figure 4b).32 The generation of reactive adjacent sites at a bimetal unit is even possible with conventional bidentate ligands such as formamidinates. Mashima, Tsurugi, and co-workers have described a quadruply bonded Mo2 paddlewheel complex that catalyzes the radical addition of the C−Cl bond of CCl4 to aliphatic olefins.33 The precatalyst contains a single, bridging triflate ligand, which is readily labilized during catalysis to open two adjacent sites at the Mo2 centers. The substrate binding sites toggle between a single, bridged Cl and two terminal Cl ligands as C−Cl bonds are activated and formed. Another interesting variation of a homometal−metalbonded cooperative catalyst is a self-assembled coordination polymer featuring linear Ag3 units, which was reported by the team lead by Wu, Hou, and Mi.34 The Ag3 polymer is an efficient heterogeneous catalyst for transforming N-tosylpyrrole and vinylcarboxylic acids into cyclopentapyrroles via tandem acylation and Nazarov cyclization. Another exciting study demonstrates that metal−metal cooperativity can even tackle the cleavage of methane’s inert C−H bonds. Studying the bimetallic carbide cluster, [Ta2C4]−, in the gas phase, He, Zhao, and their team members uncovered its activation of methane via dehydrogenation to form [(TaH)2C5]−.35 Their study paves the way for improving our understanding of methane activation on metal carbide materials. A complementary class of catalysts feature heterobimetallic pairings. These systems are attractive to researchers who seek to chart the wide space of chemical reactivity afforded by all possible metal−metal pairings. Mankad and co-workers have investigated the mechanism of their Ag−Ru catalyst (IMes)AgRuCp(CO)2 in alkyne semihydrogenation.36 A key step is the bimetallic oxidative addition of dihydrogen, which involves cleavage of the metal−metal bond to form two reactive monometallic species. Hence, this strategy departs from that employed
Figure 5. Structure of the potential Pd−Cu intermediate in the Sonogashira cross-coupling reaction with relevant bond distances.
the transient metal−metal interaction may lower the activation barrier for transmetalation, and incorporating this concept into the catalyst/ligand design may lead to improved catalysts.
■
INORGANIC CATALYSIS OF SMALL MOLECULES A long-standing societal goal is to develop catalysts for transforming small molecules of energy relevance. Following the seminal works of Gray, Nocera, and others, dirhodium complexes continue to evolve for the production of dihydrogen as an alternative fuel.40−42 Turro, Dunbar, and co-workers recently reported dirhodium catalysts with a mixed ligand set of electron-donating foramidinate and electron-accepting bipyridyl-type ligands that achieve the electrocatalytic production of dihydrogen from H+ (acetic acid) with high turnover frequencies.43 On the basis of their electrocatalytic studies, the authors propose a bimetallic mechanism featuring a key protonation of a dirhodium(II,I) species to generate a reactive dirhodium(II,III) hydride intermediate, where the hydride binds to a single Rh center. Moving up the group to cobalt, Lu, Gagliardi, and co-workers reported a dicobalt catalyst for the reductive silylation of dinitrogen to N(SiMe3)3 at ambient temperature using 1 atm of N2, KC8, and Me3SiCl and achieving turnover numbers of 195 in a single catalysis run and 320 in two sequential runs.44 Analogous to the dirhodium systems, dinitrogen binding and functionalization is predicted to occur at the axial position of a single Co center. Despite the seeming “single metalsite” reactivity, the presence of the distal cobalt metal is critical to the high catalytic activity. Switching to an isostructural Co−Al catalyst, where an Al ion substitutes the supporting Co, the turnover number dramatically drops by 6.5-fold.
■
PHOTOCHEMISTRY Catalysts that absorb sunlight to make chemical fuels will have a central role in a future built on sustainable energy. Toward this 7579
DOI: 10.1021/acs.inorgchem.7b01330 Inorg. Chem. 2017, 56, 7577−7581
Inorganic Chemistry
Editorial
John F. Berry*,† Connie C. Lu*,‡
goal, researchers have investigated dirhodium paddlewheel-type complexes because visible light can generate excited states in these species that can undergo consecutive oxidative additions of HX substrates to generate dihydrogen.40−42 Because of the stability of the M−X bonds, the most difficult step in the catalytic scheme is extrusion of the X ligands via the photoelimination of X2. A recent report by Nocera and co-workers provides additional insight into the photoelimination of Cl2 from PtIIICl3 bimetallic complexes featuring Pt2(III,III) and PtIIIRhI cores.45 The authors note that dichlorine photoelimination occurs with higher quantum yields when the two equatorial chlorine ligands are cis to each other. They explain that such a fac geometry allows facile formation of a σ-Cl2 intermediate. On the other hand, the mer isomer where the two equatorial chlorine ligands are trans leads to an energetically less favorable, stepwise elimination of two Cl• equivalents. Photolysis can also be used to access bimetallic oxo and nitride species featuring delocalized metal−metal and metal− ligand multiple bonds.46 Berry and co-workers have utilized metal−metal-bonded diruthenium complexes with oxyanion ligands as precursors to a transient Ru−RuO terminal oxo structure via photoelimination of the NO2 radical (Figure 6a).
†
■
Department of Chemistry, University of WisconsinMadison, 1101 University Avenue, Madison, Wisconsin 53706, United States ‡ Department of Chemistry, University of Minnesota, 207 Pleasant Street SE, Minneapolis, Minnesota 55455, United States
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. *E-mail:
[email protected]. ORCID
Connie C. Lu: 0000-0002-5162-9250 Notes
Views expressed in this editorial are those of the authors and not necessarily the views of the ACS.
■
REFERENCES
(1) Cotton, F. A.; Curtis, N. F.; Harris, C. B.; Johnson, B. F.; Lippard, S. J.; Mague, J. T.; Robinson, W. R.; Wood, J. S. Mononuclear and Polynuclear Chemistry of Rhenium (III): Its Pronounced Homophilicity. Science 1964, 145, 1305−7. (2) Nguyen, T.; Sutton, A. D.; Brynda, M.; Fettinger, J. C.; Long, G. J.; Power, P. P. Synthesis of a stable compound with fivefold bonding between two chromium(I) centers. Science 2005, 310, 844−847. (3) Peligot, M. E. Sur un nouvel oxyde de chrome. C. R. Acad. Sci. 1844, 19, 609−615. (4) Cotton, F. A.; Deboer, B. G.; Laprade, M. D.; Pipal, J. R.; Ucko, D. A. Multiple Chromium(II)-Chromium(II) and Rhodium(II)Rhodium(II) Bonds. J. Am. Chem. Soc. 1970, 92, 2926−2927. (5) Cotton, F. A.; Daniels, L. M.; Murillo, C. A. The 1st Complex with a σ-2-π-4 Triple Bond Between Vanadium Atoms in a Ligand Framework of Four-Fold Symmetry: V2((p-CH3C6H4)NC(H)N(pC6H4CH3))4. Angew. Chem., Int. Ed. Engl. 1992, 31, 737−738. (6) Rudd, P. A.; Liu, S. S.; Planas, N.; Bill, E.; Gagliardi, L.; Lu, C. C. Multiple Metal-Metal Bonds in Iron-Chromium Complexes. Angew. Chem., Int. Ed. 2013, 52, 4449−4452. (7) Wu, B.; Wilding, M. J. T.; Kuppuswamy, S.; Bezpalko, M. W.; Foxman, B. M.; Thomas, C. M. Exploring Trends in Metal−Metal Bonding, Spectroscopic Properties, and Conformational Flexibility in a Series of Heterobimetallic Ti/M and V/M Complexes (M = Fe, Co, Ni, and Cu). Inorg. Chem. 2016, 55, 12137−12148. (8) Enemark, J. H.; Feltham, R. D. Principles of Structure, Bonding, and Reactivity for Metal Nitrosyl Complexes. Coord. Chem. Rev. 1974, 13, 339−406. (9) Cotton, F. A.; Marler, D. O.; Schwotzer, W. Uranium-to-Uranium Bonds: Do They Exist? Inorg. Chim. Acta 1984, 85, L31−L32. (10) Hlina, J. A.; Pankhurst, J. R.; Kaltsoyannis, N.; Arnold, P. L. Metal−Metal Bonding in Uranium−Group 10 Complexes. J. Am. Chem. Soc. 2016, 138, 3333−3345. (11) Lichtenberger, N.; Wilson, R. J.; Eulenstein, A. R.; Massa, W.; Clérac, R.; Weigend, F.; Dehnen, S. Main Group Metal−Actinide Magnetic Coupling and Structural Response Upon U4+ Inclusion Into Bi, Tl/Bi, or Pb/Bi Cages. J. Am. Chem. Soc. 2016, 138, 9033−9036. (12) Zener, C. Interaction Between the d-Shells in the Transition Metals II. Ferromagnetic Compounds of Manganese with Perovskite Structure. Phys. Rev. 1951, 82, 403−405. (13) Anderson, P. W.; Hasegawa, H. Considerations on Double Exchange. Phys. Rev. 1955, 100, 675−681. (14) Hernández Sánchez, R.; Bartholomew, A. K.; Powers, T. M.; Ménard, G.; Betley, T. A. Maximizing Electron Exchange in a [Fe3] Cluster. J. Am. Chem. Soc. 2016, 138, 2235−2243. (15) Vaddypally, S.; Jovinelli, D. J.; McKendry, I. G.; Zdilla, M. J. Covalent Metal−Metal-Bonded Mn4 Tetrahedron Inscribed within a
Figure 6. Photolysis of diruthenium complexes to reveal reactive diruthenium oxo and nitrido species.
The oxo complex is able to oxidize PPh3 to OPPh3, regenerating the starting Ru−Ru−Cl complex by photoactivation of CH2Cl2.47 Although structural characterization of the proposed Ru−RuO intermediate in this work remains elusive, Powers and co-workers have utilized a photocrystallographic technique to obtain structural information on a related Ru−RuN terminal nitrido complex (Figure 6b), which had earlier been characterized spectroscopically by the Berry group.48 The terminal nitride was obtained by cryogenic photolysis of a single crystal of the corresponding Ru−Ru−N3 azido precursor complex, which generates a molecule of dinitrogen upon irradiation that remains trapped within the structure.49
■
OUTLOOK Metal−metal bonding is a classic topic in inorganic chemistry and rests solidly on 50 years of fundamental research. This virtual issue showcases only some of the recent developments in this area. Metal−metal bonds are increasingly being employed as tools for developing state-of-the-art molecular magnets and sensing materials and for addressing important challenges in biology, energy, and catalysis. The lively pursuit of both fundamentals and applications by new research teams is reinvigorating this area in innovative directions. To the existing and uninitiated practitioners of this field, the call to action is to continue to build on the foundational work to reach new audiences and tackle challenging scientific and societal problems by taking advantage of the richness of chemistry available to metal−metal bonds. 7580
DOI: 10.1021/acs.inorgchem.7b01330 Inorg. Chem. 2017, 56, 7577−7581
Inorganic Chemistry
Editorial
Four-Coordinate Manganese Cubane Cluster, As Evidenced by Unexpected Temperature-Independent Diamagnetism. Inorg. Chem. 2017, 56, 3733−3737. (16) Krogmann, K. Planar Complexes Containing Metal-Metal Bonds. Angew. Chem., Int. Ed. Engl. 1969, 8, 35−42. (17) Barton, J. K.; Rabinowitz, H. N.; Szalda, D. J.; Lippard, S. J. Synthesis and Crystal-Structure of cis-Diammine-Platinum α-Pyridone Blue. J. Am. Chem. Soc. 1977, 99, 2827−2829. (18) Uemura, K.; Uesugi, N.; Matsuyama, A.; Ebihara, M.; Yoshikawa, H.; Awaga, K. Integration of Paramagnetic Diruthenium Complexes into an Extended Chain by Heterometallic Metal−Metal Bonds with Diplatinum Complexes. Inorg. Chem. 2016, 55, 7003− 7011. (19) Guillet, J. L.; Bhowmick, I.; Shores, M. P.; Daley, C. J. A.; Gembicky, M.; Golen, J. A.; Rheingold, A. L.; Doerrer, L. H. Thiocyanate-Ligated Heterobimetallic {PtM} Lantern Complexes Including a Ferromagnetically Coupled 1D Coordination Polymer. Inorg. Chem. 2016, 55, 8099−8109. (20) Zhou, H. C.; Long, J. R.; Yaghi, O. M. Introduction to MetalOrganic Frameworks. Chem. Rev. 2012, 112, 673−674. (21) Zhang, J.; Kosaka, W.; Fukunaga, H.; Kitagawa, S.; Takata, M.; Miyasaka, H. Regulation of NO Uptake in Flexible Ru Dimer Chain Compounds with Highly Electron Donating Dopants. Inorg. Chem. 2016, 55, 12085−12092. (22) Yannello, V. J.; Fredrickson, D. C. Generality of the 18-n Rule: Intermetallic Structural Chemistry Explained through Isolobal Analogies to Transition Metal Complexes. Inorg. Chem. 2015, 54, 11385−11398. (23) Tambornino, F.; Sappl, J.; Pultar, F.; Cong, T. M.; Hübner, S.; Giftthaler, T.; Hoch, C. Electrocrystallization: A Synthetic Method for Intermetallic Phases with Polar Metal−Metal Bonding. Inorg. Chem. 2016, 55, 11551−11559. (24) Kappera, R.; Voiry, D.; Yalcin, S. E.; Branch, B.; Gupta, G.; Mohite, A. D.; Chhowalla, M. Phase-engineered low-resistance contacts for ultrathin MoS2 transistors. Nat. Mater. 2014, 13, 1128− 1134. (25) Amara, K. K.; Chen, Y.; Lin, Y.-C.; Kumar, R.; Okunishi, E.; Suenaga, K.; Quek, S. Y.; Eda, G. Dynamic Structural Evolution of Metal−Metal Bonding Network in Monolayer WS2. Chem. Mater. 2016, 28, 2308−2314. (26) Paulissen, R.; Reimlinger, H.; Hayez, E.; Hubert, A. J.; Teyssie, P. Diazocompounds II. Insertion in the Hydroxylic Bond. Tetrahedron Lett. 1973, 14, 2233−2236. (27) Doyle, M. P.; Griffin, J. H.; Bagheri, V.; Dorow, R. L. Correlation between Catalytic Reactions of Diazo-Compounds and Stoichiometric Reactions of Transition-Metal Carbenes with Alkenes Mechanism of the Cyclopropanation Reaction. Organometallics 1984, 3, 53−61. (28) Nakamura, E.; Yoshikai, N.; Yamanaka, M. Mechanism of C-H bond activation/C-C bond formation reaction between diazo compound and alkane catalyzed by dirhodium tetracarboxylate. J. Am. Chem. Soc. 2002, 124, 7181−7192. (29) Kornecki, K. P.; Briones, J. F.; Boyarskikh, V.; Fullilove, F.; Autschbach, J.; Schrote, K. E.; Lancaster, K. M.; Davies, H. M. L.; Berry, J. F. Direct Spectroscopic Characterization of a Transitory Dirhodium Donor-Acceptor Carbene Complex. Science 2013, 342, 351−354. (30) Werlé, C.; Goddard, R.; Philipps, P.; Farès, C.; Fürstner, A. Structures of Reactive Donor/Acceptor and Donor/Donor Rhodium Carbenes in the Solid State and Their Implications for Catalysis. J. Am. Chem. Soc. 2016, 138, 3797−3805. (31) Dutta, I.; Sarbajna, A.; Pandey, P.; Rahaman, S. M. W.; Singh, K.; Bera, J. K. Acceptorless Dehydrogenation of Alcohols on a Diruthenium(II,II) Platform. Organometallics 2016, 35, 1505−1513. (32) Steiman, T. J.; Uyeda, C. Reversible Substrate Activation and Catalysis at an Intact Metal−Metal Bond Using a Redox-Active Supporting Ligand. J. Am. Chem. Soc. 2015, 137, 6104−6110. (33) Rej, S.; Majumdar, M.; Kando, S.; Sugino, Y.; Tsurugi, H.; Mashima, K. Mixed Ligated Tris(amidinate)dimolybdenum Com-
plexes as Catalysts for Radical Addition of CCl4 to 1-Hexene: Leaving Ligand Lability Controls Catalyst Activity. Inorg. Chem. 2017, 56, 634−644. (34) Huang, C.; Han, X.; Shao, Z.; Gao, K.; Liu, M.; Wang, Y.; Wu, J.; Hou, H.; Mi, L. Solvent-Induced Assembly of Sliver Coordination Polymers (CPs) as Cooperative Catalysts for Synthesizing of Cyclopentenone[b]pyrroles Frameworks. Inorg. Chem. 2017, 56, 4874−4884. (35) Li, H.-F.; Zhao, Y.-X.; Yuan, Z.; Liu, Q.-Y.; Li, Z.-Y.; Li, X.-N.; Ning, C.-G.; He, S.-G. Methane Activation by Tantalum Carbide Cluster Anions Ta2C4−. J. Phys. Chem. Lett. 2017, 8, 605−610. (36) Karunananda, M. K.; Mankad, N. P. Heterobimetallic H2 Addition and Alkene/Alkane Elimination Reactions Related to the Mechanism of E-Selective Alkyne Semihydrogenation. Organometallics 2017, 36, 220−227. (37) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W. Reversible, metal-free hydrogen activation. Science 2006, 314, 1124− 1126. (38) Koppaka, A.; Yempally, V.; Zhu, L.; Fortman, G. C.; Temprado, M.; Hoff, C. D.; Captain, B. Synthesis of [Pt(SnBut3)(IBut)(μ-H)]2, a Coordinatively Unsaturated Dinuclear Compound which Fragments upon Addition of Small Molecules to Form Mononuclear Pt−Sn Complexes. Inorg. Chem. 2016, 55, 307−321. (39) Oeschger, R. J.; Chen, P. Structure and Gas-Phase Thermochemistry of a Pd/Cu Complex: Studies on a Model for Transmetalation Transition States. J. Am. Chem. Soc. 2017, 139, 1069− 1072. (40) Mann, K. R.; Lewis, N. S.; Miskowski, V. M.; Erwin, D. K.; Hammond, G. S.; Gray, H. B. Solar energy storage. Production of hydrogen by 546-nm irradiation of a dinuclear rhodium(I) complex in acidic aqueous solution. J. Am. Chem. Soc. 1977, 99, 5525−5526. (41) Heyduk, A. F.; Nocera, D. G. Hydrogen Produced from Hydrohalic Acid Solutions by a Two-Electron Mixed-Valence Photocatalyst. Science 2001, 293, 1639−1641. (42) Gray, H. B.; Maverick, A. W. Solar Chemistry of Metal Complexes. Science 1981, 214, 1201−1205. (43) White, T. A.; Witt, S. E.; Li, Z.; Dunbar, K. R.; Turro, C. New Rh2(II,II) Architecture for the Catalytic Reduction of H+. Inorg. Chem. 2015, 54, 10042−10048. (44) Siedschlag, R. B.; Bernales, V.; Vogiatzis, K. D.; Planas, N.; Clouston, L. J.; Bill, E.; Gagliardi, L.; Lu, C. C. Catalytic Silylation of Dinitrogen with a Dicobalt Complex. J. Am. Chem. Soc. 2015, 137, 4638−4641. (45) Powers, D. C.; Hwang, S. J.; Anderson, B. L.; Yang, H.; Zheng, S.-L.; Chen, Y.-S.; Cook, T. R.; Gabbaï, F. P.; Nocera, D. G. Stereoelectronic Effects in Cl2 Elimination from Binuclear Pt(III) Complexes. Inorg. Chem. 2016, 55, 11815−11820. (46) Berry, J. F. The role of three-center/four-electron bonds in superelectrophilic dirhodium carbene and nitrene catalytic intermediates. Dalton Transactions 2012, 41, 700−713. (47) Corcos, A. R.; Pap, J. S.; Yang, T.; Berry, J. F. A Synthetic Oxygen Atom Transfer Photocycle from a Diruthenium Oxyanion Complex. J. Am. Chem. Soc. 2016, 138, 10032−10040. (48) Pap, J. S.; DeBeer George, S.; Berry, J. F. Delocalized MetalMetal and Metal-Ligand Multiple Bonding in a Linear Ru-RuN Unit: Elongation of a Traditionally Short RuN Bond. Angew. Chem., Int. Ed. 2008, 47, 10102−10105. (49) Das, A.; Reibenspies, J. H.; Chen, Y.-S.; Powers, D. C. Direct Characterization of a Reactive Lattice-Confined Ru2 Nitride by Photocrystallography. J. Am. Chem. Soc. 2017, 139, 2912−2915.
7581
DOI: 10.1021/acs.inorgchem.7b01330 Inorg. Chem. 2017, 56, 7577−7581
