Low-Coordinate Boride Ligands: A True Trimetalloborane (original) (raw)
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A Linear, Anionic Dimetalloborylene Complex
Angewandte Chemie International Edition, 2008
The reduction of boron-halide bonds has attracted the attention of numerous research groups for nearly 50 years, with a view to preparing low-coordinate radical or anionic boron species. The relative ease with which the neighboring isoelectronic carbenes are prepared and the emergence of stable two-coordinate gallide anions had until recently only made the absence of the analogous "boryl anion" more conspicuous. For the most part, forays into B À X bond reduction have yielded products arising from radical-type reactions with solvent molecules (hydrogen-atom abstraction, CÀO and CÀN bond cleavage), [3j] CÀH bond insertion, [3i] or radical homocoupling and/or rearrangement. [3a,c,j, 4] The simple two-electron BÀX bond reduction of monoboron systems in the absence of these further reactions is presently limited to the borole system of Yamashita and Nozaki and their boryllithium and -magnesium complexes. However, corresponding studies on the reduction of transition-metalbound BÀX moieties do not appear in the literature, which could be explained by the assumption that boryl and borylene transition-metal complexes are less stable than their metalfree haloborane counterparts. In addition to the cationic iron borylene complexes reported by Aldridge and co-workers, a number of surprisingly stable cationic complexes with MÀB bonds have been isolated in our laboratories very recently (Scheme 1); [8] however, examples of anionic complexes containing metal-bound monoboron ligands are very rare and are limited to simple boryl complexes. The first members of the now well-established family of dimanganese borylene complexes [{L(OC) 2 Mn} 2 BA] (1: A = NMe 2 ; 2: A = tBu; a: L = h 5 -C 5 H 5 ; b: L = h 5 -C 5 H 4 Me) were synthesized in 1995, [10a] and the aminoborylene examples in particular exhibited unprecedented stability, being indefinitely stable under ambient conditions (Scheme 2). The corresponding chloroborylene complexes 3 (A = Cl), derived from the aminoborylenes by treatment with anhydrous HCl, were notably less stable but resistant to brief handling in air. [10b] Aminoborylenes 1 were found to react cleanly only with strong acids, and complexes 3 react with a range of different nucleophiles, whereas the less synthetically accessible complex 2 a has been shown to react with the weaker nucleophile PCy 3 (Cy = cyclohexyl) to produce the terminal borylene complex [(h 5 -C 5 H 5 )(OC) 2 Mn=BtBu] (4). [10g] It was thought, given their substantial stability, that the chemical reduction of chloroborylene complexes 3 could yield stable and useful anionic species.
Synthesis and ligand substitution of tri-metallic triply bridging borylene complexes
Journal of Organometallic Chemistry, 2018
To build upon our earlier results of heterometallic metallaboranes employing metal carbonyls, we performed the reaction of nido-[(Cp*Rh) 2 B 3 H 7 ] (1) (nido-1) with [M(CO) 5 •THF] (M = Mo or W) that yielded the trimetallic metallaborane clusters [(Cp*Rh) 2 M(CO) 3 (µ-CO)(µ 3-BH)(B 2 H 4)] (3: M = Mo; 4: M = W) having a capped borylene fragment and trimetallic triply bridging borylene complexes [(Cp*Rh) 2 (µ 3-BH)(µ-CO)M(CO) 5 ] (5: M = Mo; 6: M = W). The chemistry of trimetallic triply bridging borylene complexes (5 and 6) were explored with Lewis bases such as tert-butyl isocyanide and bisphosphine ligands. Photolysis of 5 and 6 with tert-butyl isocyanide yielded [(Cp*Rh) 2 (µ 3-BH)(µ-CO)M(CO) 4 (CN-t Bu)] (7: M = Mo; 8: M = W) and with phosphines, PPh 2 (CH 2) n PPh 2 (n = 1, 2) they resulted in the formation of [(Cp*Rh) 2 (µ 3-BH)(µ-CO)M(CO) 4 ((PPh 2) 2 (CH 2) n)] (9: n = 1, M = Mo; 10: n = 1, M = W; 11: n = 2, M = Mo; 12: n = 2, M = W). All the new compounds have been characterized in solution by mass spectrometry and NMR spectroscopic techniques. The structural aspects were unambiguously established by X-ray crystallographic analysis of 3-4 and 7-10. 1. Introduction During the past two decades a library of metallaborane compounds with diverse geometries have been developed.[1-2] Typically there are two major approaches for the cluster build up reaction in metallaborane chemistry. For example i) metathesis reaction using monoborane reagents,[3-4] and 1 with [M(CO) 5 •THF] (M = Mo and W) which led to the formation of [(Cp*Rh) 2 M(CO) 3 (µ-CO)(µ 3-BH)(B 2 H 4)] (3: M = Mo, 4: M = W) bearing a capped borylene unit and triply bridging borylene complexes [(Cp*Rh) 2 (µ 3-BH)(µ-CO)M(CO) 5 ] (5: M = Mo, 6: M = W). Further, the reactivity of compounds 5 and 6 with CN-t Bu and bisphosphine ligands have been explored.
Angewandte Chemie International Edition, 2014
A series of novel Cp*-based (Cp* = h 5-C 5 Me 5) agostic, bis(s-borate), and boratrane complexes have been synthesized from diruthenium and dirhodium analogues of pentaborane(9). The synthesis and structural characterization of the first neutral ruthenadiborane(6) analogue are also reported. This new route offers a very efficient method for the isolation of bis(s-borate) and agostic complexes from diruthenapentaborane(9). The field of transition-metal-boron chemistry, comprising a wide range of compounds from higher-nuclearity metallaborane clusters to complexes with a single boron atom, has undergone a renaissance over the past few decades. [1, 2] Complexes with a wide variety of coordination modes have been isolated and structurally characterized, [1-5] for example, s-borane, [3, 4] boryl, [1a] and borylene complexes, [1a] metallaboranes, [1b, 2] metallaboratranes, [5] and more. [1a, 3c, 4b] Among the various novel types recognized, the electron-precise transition-metal agostic and s-borane complexes (Scheme 1), in which borane s-donation to the metal center dominates over p-back-donation, have been a subject of regular importance. [3, 4, 6] However, the lack of a simple and practical Scheme 1. Various modes of metal-boron interaction.
New Trinuclear Complexes of Group 6, 8, and 9 Metals with a Triply Bridging Borylene Ligand
Chemistry - A European Journal, 2016
Trinuclear complexeso fg roup 6, 8, and 9t ransition metals with a(m 3-BH) ligand [(m 3-BH)(Cp*Rh) 2 (m-CO)M'(CO) 5 ], 3 and 4 (3:M ' = Mo; 4:M ' = W) and 5-8, [(Cp*Ru) 3 (m 3-CO) 2 (m 3-BH)(m 3-E)(m-H){M'(CO) 3 }] (5:M ' = Cr,E = CO; 6:M ' = Mo, E = CO; 7:M ' = Mo, E = BH; 8:M ' = W, E = CO), have been synthesized from the reaction between nido-[(Cp*M) 2 B 3 H 7 ](nido-1:M = Rh; nido-2:M = RuH, Cp* = h 5-C 5 Me 5)a nd [M'(CO) 5 •thf] (M' = Mo and W). Compounds 3 and 4 are isoelectronic and isostructuralw ith [(m 3-BH)(Cp*Co) 2 (m-CO)M'(CO) 5 ], (M' = Cr,M oa nd W) and [(m 3-BH)(Cp*Co) 2 (m-CO)(m-H) 2 M''H(CO) 3 ], (M'' = Mn and Re). All compounds are composed of ab ridging borylene ligand (BÀH) that is effectively stabilized by at rinuclearf ramework. In contrast, the reactiono fnido-1 with [Cr(CO) 5 •thf] gave [(Cp*Rh) 2 Cr(CO) 3 (m-CO)(m 3-BH)(B 2 H 4)] (9). The geometry of 9 can be viewed as ac ondensed polyhedron composed of [Rh 2 Cr(m 3-BH)] and [Rh 2 CrB 2 ], atetrahedral andasquare pyramidal geometry,respectively.T he bonding of 9 can be considered by using the polyhedralf usion formalism of Mingos. Allc ompounds have been characterized by using differents pectroscopics tudies and the molecular structures were determined by using single-crystal X-ray diffraction analysis.
Angewandte Chemie (International ed. in English), 2016
We report the synthesis of the first 1,1'-bis(boratabenzene) species by tetrabromodiborane(4)-induced ring-expansion reactions of cobaltocene. Six equivalents of cobaltocene are required as the species plays the dual role of reagent and reductant to yield [{(η(5) -C5 H5 )Co}2 {μ:η(6) ,η(6) -(BC5 H5 )2 }]. The formally dianionic bis(boratabenzene) moiety with a boron-boron single bond can be viewed as a symmetric dimer of the parent boratabenzene anion as well as the first example of a diboron analogue of biphenyl. The solution electrochemistry of the bimetallic complex shows four stepwise redox events, indicating significant intramolecular interaction between the cobalt ions across the 1,1'-bis(boratabenzene) unit. The magnetic properties, as investigated by variable-temperature SQUID magnetometry, reveal weak intramolecular antiferromagnetic interactions. Density functional theory calculations support the experimental results and add insight into the various electronic stat...