A. Stock, N. N. Greenwood, A. Earnshaw, E. C. Neeve, S. J. Geier et al., Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse, Hydrides of Boron and Silicon, vol.116, pp.9091-9161, 1933.

G. J. Irvine, M. J. Lesley, T. B. Marder, N. C. Norman, C. R. Rice et al.,

G. Roper, W. R. Whittell, G. R. Wright, L. J. Bontemps, S. Vendier et al., Transition Metal?Boryl Compounds: Synthesis, Reactivity, and Structure, Chem. Rev, vol.98, pp.2685-2722, 1998.

, Chem. Soc, vol.136, pp.4419-4425, 2014.

T. Ishiyama, N. Matsuda, N. Miyaura, A. Suzuki, R. T. Baker et al., Platinum(0)-catalyzed diboration of alkynes, J. Am. Chem. Soc, vol.115, pp.11018-11019, 1993.

B. Westcott, S. A. Mann, G. John, K. D. Baker, and R. T. , Platinum-Catalyzed Diboration Using a Commercially Available Catalyst: Diboration of Aldimines to ?-Aminoboronate Esters, Angew. Chem. Int. Ed, vol.34, pp.1336-1338, 1995.

D. S. Laitar, P. Müller, and J. P. Sadighi, Efficient Homogeneous Catalysis in the Reduction of CO 2 to CO, J. Am. Chem. Soc, vol.2, pp.17196-17197, 2000.

T. Ishiyama and N. Miyaura, Metal-catalyzed reactions of diborons for synthesis of organoboron compounds, Chem. Rec, vol.3, pp.271-280, 2004.

S. K. Ritter, Boron chemistry branches out, Chem. Eng. News, vol.94, pp.20-23, 2016.

G. J. Irvine, M. J. Lesley, T. B. Marder, N. C. Norman, C. R. Rice et al.,

G. Roper, W. R. Whittell, G. R. Wright, L. J. Westcott, S. A. Fernández et al., Transition Metal?Boryl Compounds: Synthesis, Reactivity, and Structure, Adv. Organomet. Chem, vol.98, pp.39-89, 1998.

H. Braunschweig, T. Wagner, H. Braunschweig, M. Colling, C. Hu et al., From Classical to Nonclassical Metal-Boron Bonds: Synthesis of a Novel Metallaborane, Angew. Chem. Int. Ed, vol.34, pp.4352-4355, 1995.

H. D. Kaesz, W. Fellmann, G. R. Wilkes, and L. F. Dahl, A New Type of ElectronDeficient Compound. A Polyborane Hydridomanganese Carbonyl, HMn, vol.3, p.10

N. Arnold, H. Braunschweig, R. D. Dewhurst, W. C. Ewing, D. Sharmila et al., Unprecedented Borane, Diborane(3), Diborene, and Borylene Ligands via Pt-Mediated Borane Dehydrogenation, J. Am. Chem. Soc, vol.87, pp.5074-5083, 1965.

M. Hata, Y. Kawano, and M. Shimoi, Synthesis and Structure of a Dichromatetraborane Derivative

H. Braunschweig, A. Damme, R. D. Dewhurst, and A. Vargas, Bond-strengthening ? backdonation in a transition-metal ?-diborene complex, Inorg. Chem, vol.37, pp.115-121, 1998.

S. R. Wang, D. Prieschl, J. D. Mattock, M. Arrowsmith, C. Pranckevicius et al.,

, Angew. Chem., Int. Ed, vol.55, pp.12722-12726, 2016.

C. Ting and L. Messerle, Borohydride boron-hydrogen activation and dimerization by a doubly bonded, early-transition-metal organodimetallic complex. Ditantalladiborane syntheses as models for dehydrodimerization of methane to ethane, J. Am. Chem. Soc, vol.111, pp.3449-3450, 1989.

H. Brunner, G. Gehart, W. Meier, J. Wachter, B. Wrackmeyer et al.,

S. K. Bose, K. Geetharani, V. Ramkumar, S. M. Mobin, and S. Ghosh, Fine Tuning of Metallaborane Geometries: Chemistry of Metallaboranes of Early Transition Metals Derived from Metal Halides and Monoborane Reagents, J. Organomet. Chem, vol.436, pp.13483-13490, 1992.

D. K. Mondal, B. Yuvaraj, K. Arivazhagan, C. Saha, K. Varghese et al., Agostic versus Boratrane Complexes, Reactivity of Diruthenium and Dirhodium Analogues of Pentaborane, vol.53, pp.2873-2877, 2014.

B. Mondal, R. Bag, S. Ghorai, K. Bakthavachalam, E. D. Jemmis et al., Structure, Bonding, and Reactivity of Metal Complexes Comprising Diborane

;. Diborene and W. Mo-;-m=mo, CO) 2 } 2 {?-? 2 :? 2 -B 2 H 4 }] and, Angew. Chem. Int. Ed, vol.57, issue.2, pp.8079-8083, 2018.

P. D. Grebenik, M. L. Green, M. A. Kelland, J. B. Leach, and P. Mountford, Terminal substitution and cage incorporation of an ?-cyclopentadienyl ring into borane cage structures; crystal structures of

A. K. Saxena, N. S. Hosmane, T. P. Fehlner, and J. D. Kennedy, Recent advances in the chemistry of carborane metal complexes incorporating d-and fblock elements, Progress in Inorganic Chemistry, vol.93, pp.2643-2651, 1989.

A. De, Q. Zhang, B. Mondal, L. F. Cheung, S. Kar et al.,

L. Wang and S. Ghosh, Cp 2 M) 2 B 9 H 11 ] (M = Zr or Hf): early transition metal 'guarded' heptaborane with strong covalent and electrostatic bonding, Chem. Sci, vol.9, 1976.

S. K. Bose, K. Geetharani, B. Varghese, S. M. Mobin, and S. Ghosh, Metallaboranes of the Early Transition Metals: Direct Synthesis and Characterization of [{(? 5 -C 5 Me 5 )Ta} 2 B n H m ] (n=4, m=10; n=5, m=11)

. J. Eur, R. S. Dhayal, K. K. Chakrahari, B. Varghese, and S. Mobin, , vol.14, pp.9058-9064, 2008.

M. Ghosh and S. , Chemistry of Molybdaboranes: Synthesis, Structures, and Characterization of a New Class of Open-Cage Dimolybdaheteroborane Clusters, Inorg. Chem, vol.49, pp.7741-7747, 2010.

S. K. Bose, K. Geetharani, S. Sahoo, K. H. Reddy, B. Varghese et al., Synthesis, Characterization, and Electronic Structure of New Type of Heterometallic Boride Clusters, Inorg. Chem, vol.50, issue.21, pp.9414-9422, 1975.

T. P. Fehlner, J. Halet, and J. Saillard, Molecular Clusters. A Bridge to Solid-State Chemistry, Boranes and Metalloboranes: Structure,Bonding and Reactivity, 2007.
URL : https://hal.archives-ouvertes.fr/hal-00354899

E. Horwood, H. Chichester-;-yan, A. M. Beatty, and T. Fehlner, , 1990.

P. Reactivity and . Dimetallapentaboranes-nido, with Alkynes: Insertion to Form a Ruthenacarborane (M=RuH) versus Catalytic Cyclotrimerization to Form Arenes (M=Rh)

S. K. Bose, K. Geetharani, S. Ghosh, K. Geetharani, S. Tussupbayev et al., C-H activation of arenes and heteroarenes by early transition metallaborane, Cp* = ? 5 -C 5 Me 5 ), vol.40, pp.11996-11998, 2001.

. Diruthenaborane, Cp*RuCO) 2 B 2 H 6 ] as an Active Alkyne-Cyclotrimerization Catalyst

. J. Eur, Á. Álvarez, R. Macías, J. Bould, M. J. Fabra et al., Alkene Hydrogenation on an 11-Vertex Rhodathiaborane with Full Cluster Participation, J. Am. Chem. Soc, vol.18, pp.11455-11466, 2008.

K. Wade, The structural significance of the number of skeletal bonding electron-pairs in carboranes, the higher boranes and borane anions, and various transition-metal carbonyl cluster compounds, J. Chem. Soc. D, Chem. Commun, vol.0, pp.1-66, 1971.

M. A. Fox, K. Wade, E. D. Jemmis, M. M. Balakrishnarajan, and P. D. Pancharatna, A Unifying ElectronCounting Rule for Macropolyhedral Boranes, Metallaboranes, and Metallocenes, Pure Appl. Chem, vol.75, issue.24, pp.1315-1323, 2003.

E. D. Soc-;-jemmis, M. M. Balakrishnarajan, and P. D. Pancharatna, Electronic Requirements for Macropolyhedral Boranes, Chem. Rev, vol.123, pp.93-144, 2001.

T. P. Fehlner, G. A. Olah, K. Wade, R. E. Williams, and J. D. Kennedy, Disobedient Skeletons, The Borane, Carborane, Carbocation Continuum, p.85, 1991.

, Coord. Chem. Rev, vol.231, pp.23-46, 2002.

B. Mondal, R. Bag, S. Ghosh, W. ;-m-=-mo, B. Mondal et al., Synthesis, Structures, and Characterization of Dimeric Neutral Dithiolato-Bridged Tungsten Complexes, Cp*M) 2 B 4 H 10, vol.37, p.3, 2017.

, and Cp* = ? 5 -C 5 Me 5 ). Dalton Trans, vol.45, pp.10999-11007, 2016.

, Ru 2 ] bridging ring is an oblato-closo cluster, Chem. commun, vol.51, pp.3828-3831, 2015.

A. Thakur, K. K. Chakrahari, B. Mondal, S. Ghosh, S. Sahoo et al., Novel Triple-Decker Sandwich Complex with a Six-Membered, Chlorinated Hypoelectronic Dimetallaborane Clusters: Synthesis, Characterization, and Electronic Structures of (? 5 -C 5 Me 5 W) 2 B 5 H n Cl m (n = 7, vol.52, pp.6509-6516, 2009.

S. Aldridge, M. Shang, and T. P. Fehlner, Synthesis of Novel Molybdaboranes from (? 5 -C 5 R 5 )MoCl n Precursors (R = H, Me; n = 1, 2, 4), J. Am. Chem. Soc, vol.120, pp.2586-2598, 1998.

R. S. Dhayal, S. Sahoo, K. H. Reddy, S. M. Mobin, E. D. Jemmis et al.,

, Vertex-Fused Metallaborane Clusters: Synthesis, Characterization and Electronic Structure of

, Inorg. Chem, vol.49, pp.900-904, 2010.

S. A. Snow, M. Shimoi, C. D. Ostler, B. K. Thompson, G. Kodama et al.,

, Inorg. Chem, vol.23, pp.511-512, 1984.

K. Katoh, M. Shimoi, and H. Ogino, Syntheses and structures of

, Inorg. Chem, vol.31, pp.670-675, 1992.

W. I. Bailey, M. H. Chisholm, F. A. Cotton, L. A. Rankel, M. Fleischmann et al., Reactions of metal-tometal multiple bonds. 4. .mu.-Acetylene-bis(cyclopentadienyl)tetracarbonyldimolybdenum compounds. Preparations, properties, structural characterizations, and dynamical solution behavior, J. Am. Chem. Soc, vol.100, pp.5764-5773, 1978.

, Dalton Trans, vol.45, pp.13742-13749, 2016.

C. Jun, J. Halet, A. L. Rheingold, and T. P. Fehlner, Preparation and Characterization of Cobaltaboranes Containing Cobalt Carbonyl Fragments, Inorg. Chem, vol.34, pp.2101-2107, 1995.

D. M. Mingos, A General Theory for Cluster and Ring Compounds of the Main Group and Transition Elements, Nat. Phys. Sci, vol.236, issue.33, pp.3615-3616, 1972.

S. Aldridge, T. P. Fehlner, and M. Shang, Directed Synthesis of Chromium and Molybdenum Metallaborane Clusters. Preparation and Characterization of (Cp*Cr) 2 B 5 H 9, J. Am. Chem. Soc, vol.119, pp.2339-2340, 1997.

A. S. Weller, M. Shang, and T. P. Fehlner, Synthesis of Mono-and Ditungstaboranes from

, Reaction Pathway by Choice of Monoboron Reagent and Oxidation State of Metal Center, Organometallics, vol.18, pp.53-64, 1999.

, Computed 11 B NMR chemical shifts (for 3' and 5

, employing GIAO method satisfactorily helped us to assign all the boron atoms with a margin of error ~10 ppm, whereas, for 5' (the Cp analogue of 5) ca. 40 ppm error was observed (see Table S1)

X. Lei, M. Shang, and T. P. Fehlner, 2?-commo-Bis[2-ruthena-nido-1-(?5-pentamethylcyclopentadienyl)ruthenahexaborane(12)]: An Unusual Ruthenaborane Related to Ruthenocene and Exhibiting a Linear Triruthenium Fragment, Angew. Chem. Int. Ed, vol.2, 1986.

J. Corbett, Extended metal-metal bonding in halides of the early transition metals

J. D. Kennedy, The Polyhedral Metallaboranes Part I, Acc. Chem. Res, vol.14, pp.239-246, 1981.

, Metallaborane Clusters with Seven Vertices and Fewer, Prog. Inorg. Chem, vol.32, pp.519-679, 1984.

J. D. Kennedy, S. Ghosh, T. P. Fehlner, and B. Noll, Metallaborane Clusters with Eight Vertices and More, Prog. Inorg. Chem, vol.34, pp.211-434, 1986.

C. , Condensed metallaborane clusters: synthesis and structure of Fe, vol.2, p.6

K. Ru-;-wong, J. R. Bowser, J. R. Pipal, and R. N. Grimes, Tetracarbon metallocarboranes. 5. A new synthetic route: synthesis of Co 2 C 4 B 6 structure of (? 5 -C 5 H 5 ) 2 Co 2 C 4 B 6 H 10, J. Am. Chem. Soc, vol.100, pp.5045-5051, 1978.

D. M. Mingos and R. N. Grimes, Cluster forming and cage fusion in metallacarborane chemistry, Acc. Chem. Res, vol.17, pp.311-319, 1984.

J. D. Kennedy, Advances in, vol.143, pp.71-96, 1995.

W. Siebert and . Ed, , p.451, 1997.

, This can be explained qualitatively as; W3 is in bonding contact with W1, W2, B4 and two hydride ligands that contributes total of 5 electrons which is equal to that of a ?5-Cp or Cp* ligand

Y. Wang, B. Quillian, P. Wei, C. S. Wannere, Y. Xie et al.,

P. V. Schleyer and G. H. Robinson, b) Scheschkewitz, D. A Base-Stabilized Neutral B=B Bond: Closing a Gap by Filling the Void, Angew. Chem. Int. Ed, vol.129, pp.12412-12413, 1995.

Y. Wang, B. Quillian, P. Wei, Y. Xie, C. S. Wannere et al.,

P. V. Schleyer, G. H. Robinson, T. Planar, T. Wang, Y. Robinson et al., Carbene Stabilization of Highly Reactive Main-Group Molecules, Conformational Flexibility of Neutral Diborenes, vol.130, pp.11815-11832, 2008.

M. P. Mitoraj and A. Michalak, Multiple Boron?Boron Bonds in Neutral Molecules: An Insight from the Extended Transition State Method and the Natural Orbitals for Chemical Valence Scheme, Inorg. Chem, vol.50, pp.2168-2174, 2011.

D. Single, Triple Bonds and Chains: The Formation of Electron-Precise B-B Bonds

H. Braunschweig, R. D. Dewhurst, J. Brand, H. Braunschweig, S. S. Sen et al., e) Fischer, R. C.; Power, P. P. ?-Bonding and the Lone Pair Effect in Multiple Bonds Involving Heavier Main Group Elements: Developments in the New Millennium, (f) Power, P. P. Interaction of Multiple Bonded and Unsaturated Heavier Main Group Compounds with Hydrogen, Ammonia, Olefins, and Related Molecules, vol.52, pp.3877-3923, 2010.

. Res, , vol.44, pp.627-637, 2011.

H. Hashimoto, M. Shang, T. P. Fehlner, S. Aldridge, H. Hashimoto et al., Clusters as Ligands. Coordination of an Electronically Unsaturated Chromaborane to an Iron Tricarbonyl Fragment, J. Am. Chem. Soc, vol.118, pp.8164-8165, 1996.

P. Cluster, Expansion Reactions of Group 6 Metallaboranes. Syntheses, Crystal Structures, and

, Cp*Cr) 2 B 4 H 8 Fe(CO) 3 , (Cp*Cr) 2 B 4 H 7 Co (CO) 3 , and (Cp*Mo) 2 B 5 H 9 Fe(CO) 3, Spectroscopic Characterizations of (Cp*Cr) 2 B 5 H 9, vol.37, pp.928-940, 1998.

L. B. Handy, J. K. Ruff, L. F. Dahl, O. J. Scherer, H. Sitzmann et al., Structural characterization of the dinuclear metal carbonyl anions [M 2 (CO) 10 ] 2-(M = chromium, molybdenum) and [Cr 2 (CO) 10 H] -. Marked stereochemical effect of a linearly protonated metal-metal bond, J. Am. Chem. Soc, vol.92, pp.7312-7326, 1970.

, Mo?Mo(CO) 2 (? 5 -C 5 H 5 ) zu den tetraedrischen molybdänkomplexen P n, C 5 H 5 )(CO), vol.268, pp.9-12, 1984.

R. S. Dahyal, S. Sahoo, V. Ramkumar, and S. Ghosh, Substitution at boron in molybdaborane frameworks: Synthesis and characterization of isomeric (? 5 -C 5 Me 5 Mo) 2 B 5 H n X m (when X=Cl: n=5, 7, 8; m=4, 2, 1 and X=Me: n=6, 7; m=3, 2), J. Organomet. Chem, vol.694, 2009.

R. X-=-br, ). Pri, and X. ,

, Cl, vol.4

, J. Chem. Soc. Dalton Trans, pp.3793-3800, 1990.

M. Kaushika, A. Singh, and M. Kumar, The chemistry of group-VIb metal carbonyls, Eur. J. Chem, vol.3, pp.367-394, 2012.

G. E. Ryschkewitsch, K. C. Nainan, and . Octahydrotriborate,

. Gaussian-09 and M. J. Frisch, , 2010.

H. L. Schmider and A. D. Becke, b) Perdew, J. P. Density-functional approximation for the correlation energy of the inhomogeneous electron gas, J. Chem. Phys, vol.108, pp.8822-8824, 1986.

F. Weigend and R. Ahlrichs, Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy, Phys. Chem

, Chem. Phys, vol.7, pp.3297-3305, 2005.

D. Andrae, U. Häußermann, M. Dolg, H. Stoll, and H. Preuss, Energy-adjustedab initio pseudopotentials for the second and third row transition elements, Theor. Chim. Acta, vol.77, pp.123-141, 1990.

A. D. Becke, C. Lee, W. Yang, and R. G. Parr, Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density, Phys. Rev. A, vol.38, pp.785-789, 1988.

, The role of exact exchange, J. Chem. Phys, vol.98, pp.5648-5651, 1993.

F. London, K. Wolinski, J. F. Hinton, and P. Pulay, Efficient implementation of the gauge-independent atomic orbital method for NMR chemical shift calculations, J. Am. Chem. Soc, vol.8, pp.8251-8260, 1937.

E. D. Glendening, A. E. Reed, and J. E. Carpenter,

T. Madison-;-reed, A. E. Weinhold, F. Curtiss, L. A. Weinhold, F. Landis et al., Intermolecular interactions from a natural bond orbital, donor-acceptor viewpoint, Valency and bonding: A natural bond orbital donor-acceptor perspective, vol.88, pp.899-926, 1988.

U. , , 2005.

K. B. Wiberg, Application of the pople-santry-segal CNDO method to the cyclopropylcarbinyl and cyclobutyl cation and to bicyclobutane, Tetrahedron, vol.24, pp.1083-1096, 1968.

R. F. Bader, Atoms in Molecules: a Quantum Theory

U. K. Oxford, R. F. Bader, . Bond, and R. F. Bader, A quantum theory of molecular structure and its applications, J. Phys. Chem. A, vol.102, pp.893-928, 1990.

T. Lu and F. Chen, Multiwfn: A multifunctional wavefunction analyzer, J. Comput. Chem, vol.33, pp.580-592, 2012.

. Bruker, APEX2, SAINT and SADABS, 2004.

G. M. Sheldrick, SHELXS-97, 1997.

G. M. Sheldrick, For Table of Contents Only Use of Single Metal Fragments for Cluster Building: Synthesis, Structure and Bonding of Heterometallaboranes Using CO gas we have synthesized an extremely fluxional molybdenum diborane(4) species, [{Cp*Mo(CO) 2 } 2 {µ-? 2 :? 2 -B 2 H 4 }] that mimic Cotton's dimolybdenum-acetylene complex, addition, we have isolated and structurally characterized a homoleptic molybdaborane, p.3