DOI: 10.1002/cplu.201400013 Metallaboranes from Metal Carbonyl Compounds and Their Utilization as Catalysts for Alkyne Cyclotrimerization V. P. Anju, SubratKumar Barik, Bijnaneswar Mondal, V. Ramkumar, and Sundargopal Ghosh* [a] Introduction Organometallic chemistry can be regarded as the confluence of coordination chemistry and organic chemistry. The mutually synergistic interactions of metals with organic ligands or frag- ments and vice versa created new chemistries of both funda- mental and practical importance. [1–3] On the other hand, some- what earlier, metallaborane chemistry provided a close link with organometallic systems, and hence, was rationalized with the 18 electron rule. [4–9] Indeed, many of these clusters, gener- ated from organometallic compounds by replacing C with B plus B H B bridging hydrogen atoms, could be related to sev- eral classic organometallic complexes that define basic struc- tural and bonding paradigms, for example, [(CO) 4 Fe(h 2 -C 2 H 4 )] versus [{(CO) 4 Fe}B 2 H 5 ]  , [10] [(PR 3 )ClPd(h 3 -C 3 H 5 )] versus [{(PR 3 ) 2 Pd}B 3 H 7 ], [11] [(h 5 -C 5 H 5 )Co(h 4 -C 4 H 4 )] versus [{(h 5 - C 5 H 5 )Co}B 4 H 8 ], [12] [(h 5 -C 5 H 5 )Fe(h 5 -C 5 H 5 )] versus [{(h 5 - C 5 H 5 )Fe}B 5 H 10 ], [13] and [(Cp*Ru)B 8 H 14 (RuCp*)] versus [Cp*Ru- (C 8 H 6 )RuCp*] [14] (Scheme 1). In addition, although the transition metal fragments can be isolobal to borane fragments, they possess bonding capabilities that extend beyond this isolobal analogy. [15–17] The pioneering studies of Hawthorne and Grimes on the synthesis of metallacarboranes has paved the way for develop- ment in the field of metallaborane chemistry. Successively, the contributions of Fehlner, [4, 6] Green, [18, 19] Kennedy, [7, 20] and others [9, 21, 22] have made significant impacts in this field, which has attracted significant attention owing to the uncommon structures involved as well as their unique bonding, uneven degrees of reactivity, and catalytic activity. [6, 18–27] The earliest synthesis methods for metallaboranes were thermolysis or The photolysis of [M 2 (CO) 10 ] (M = Re or Mn) with BH 3 ·thf at room temperature yields arachno-1 and 2, [(CO) 8 M 2 B 2 H 6 ](1: M = Re, 2 :M = Mn). Both the compounds show a butterfly structure with seven skeletal electron pairs and 42 valence electrons. This result presents a new method for general access to low-boron-content metal–boron compounds without the cyclopentadienyl ligand at the metal centers. This new syn- thetic route is superior to the existing procedures because it avoids the use of [LiBH 4 ] and metal polychlorides, for which the synthesis is very tedious. Compound 1 catalyzes the cyclo- trimerization of a series of internal and terminal alkynes to yield mixtures of 1,3,5- and 1,2,4-substituted benzenes. The re- activity of 1 with alkynes demonstrates for the first time that the introduction of the [B 2 H 6 ] moiety into the [Re 2 (CO) 10 ] framework significantly enhances the catalytic activity. Note that [Re 2 (CO) 10 ] catalyzes the same set of alkynes under harsh conditions over a prolonged period of time. Quantum-chemi- cal calculations using DFT methods are applied to afford fur- ther insight into the electronic structure, stability, and bonding of 1 and 2. All the compounds are characterized by IR and 1 H, 11 B, and 13 C NMR spectroscopy, and the geometry of 1 is estab- lished unambiguously through crystallographic analysis. Scheme 1. Metallaborane analogues to p ligands in organometallic com- plexes. Cp = h 5 -C 5 H 5 . [(CO) 4 Fe(h 2 -C 2 H 4 )] (I), [{(CO) 4 Fe}B 2 H 5 ]  (II), [(PR 3 )ClPd(h 3 - C 3 H 5 )] (III), [{(PR 3 ) 2 Pd}B 3 H 7 ] (IV), [(h 5 -C 5 H 5 )Co(h 4 -C 4 H 4 )] (V), [{(h 5 -C 5 H 5 )Co}B 4 H 8 ] (VI), [(h 5 -C 5 H 5 )Fe(h 5 -C 5 H 5 )] (VII), [{(h 5 -C 5 H 5 )Fe}B 5 H 10 ] (VIII), [(Cp*Ru)B 8 H 14 - (RuCp*)] (IX), [Cp*Ru(C 8 H 6 )RuCp*] (X). [a] V.P. Anju, S. K. Barik, B. Mondal, V. Ramkumar, Prof. S. Ghosh Department of Chemistry Indian Institute of Technology Madras Chennai 600036 (India) Fax:(+91) 4422574202 E-mail : sghosh@iitm.ac.in Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cplu.201400013.  2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim ChemPlusChem 2014, 79, 546 – 551 546 CHEMPLUSCHEM FULL PAPERS