Shaowu Du

Alkyne coupling at a rhenium–monocarborane substrate: synthesis of Re,B-η2:σ-butadienyl complexes

Treatment of 7-NH2But-nido-7-CB10H12 in tetrahydrofuran (THF) with LiBun (3 equiv) and then [ReBr(CO)3(THF)2] gives the rhenacarborane dianion [1-NHBut-2,2,2-(CO)3-closo-2,1-ReCB10H10]2−, isolated as the bis-[N(PPh3)2]+ salt (4). Iodine oxidation of this ReI intermediate gives the ReIII complex [1,2-µ-NHBut-2,2,2-(CO)3-closo-2,1-ReCB10H10] 6 in which the carborane functions formally as an 8-electron (6π + 2σ) donor. Reaction of 6 with ligands L in the presence of Me3NO gives substituted products [1,2-µ-NHBut-2,2-(CO)2-2-L-closo-2,1-ReCB10H10] [L = PPh3 (7a), CNXyl (7b; Xyl = C6H3Me2-2,6), or ButCCH (7c)]. Formation of complex 7c is unexpectedly accompanied by [1,2-µ-NHBut-2,2-(CO)2-3,2-σ:η2-{C(CHBut)–CHCHBut}-closo-2,1-ReCB10H9] 8a, in which an alkyne-derived dienyl group is bound to both the rhenium centre and to an adjacent boron vertex. Complex 8a is also obtained from 7c with ButCCH and Me3NO. The same reaction of 7c, using PhCCH or CNXyl instead of ButCCH, gives, respectively, [1,2-µ-NHBut-2,2-(CO)2-3,2-σ:η2-{C(CHBut)–CHCHPh}-closo-2,1-ReCB10H9] 8b and [1,2-µ-NHBut-2-ButCCH-2-CO-2-CNXyl-closo-2,1-ReCB10H10] 9. Addition of donors L to 8a results in displacement from rhenium of the pendant dienyl moiety, yielding [1,2-µ-NHBut-2,2-(CO)2-2-L-3-{C(CHBut)–CHCHBut}-closo-2,1-ReCB10H9] [L = PMe3 (10a), CNBut (10b)]. Single-crystal X-ray diffraction analyses have confirmed the novel structural features of compounds 6, 7c, 8b and 9.

Synthesis and reactivity of icosahedral molybdenum-monocarbaborane complexes containing one or two intramolecular amino bridges

The room-temperature reaction of Li2[7-NMe3-nido-7-CB10H10] with [Mo(CO)4{NH(CH2)5}2] in THF (THF = tetrahydrofuran), followed by oxidation with CF3SO3Me or CH2CHCH2Br, gives the anion [2,3-µ-{N(CH2)5}-2,2,2-(CO)3-closo-2,1-MoCB10H10]−, isolated as the [N(PPh3)2]+ salt 3a. This salt may similarly be isolated following the direct reaction of 7-NMe3-nido-7-CB10H12 with [Mo(CO)4{NH(CH2)5}2] in refluxing THF. An X-ray diffraction study confirmed the absence of the C–NMe3 group in the anion and formation of an intramolecular piperidinyl bridge between molybdenum and boron. The related compound [N(PPh3)2][1-NH2-2,3-µ-{N(CH2)5}-2,2,2-(CO)3-closo-2,1-MoCB10H9] 4 is obtained from Li[7-NH2-nido-7-CB10H12] with [Mo(CO)4{NH(CH2)5}2] in refluxing THF. Treatment of 3a or 4 with {M(PPh3)}+ (M = Cu, Ag) yields heterobimetallic complexes containing direct Mo–M bonds, of which [2,7,11-{Cu(PPh3)}-7,11-(µ-H)2-2,3-µ-{N(CH2)5}-2,2,2-(CO)3-closo-2,1-MoCB10H8] has been studied by X-ray diffraction analysis. In THF solution, 4 is oxidized by iodine or N-chlorosuccinimide affording the MoIV species [1,2-µ-NH2-2,3-µ-{N(CH2)5}-2,2-(CO)2-2-X-closo-2,1-MoCB10H9] (X = I, Cl, respectively). An X-ray diffraction study of the iodo derivative showed that it contained two intramolecular amino bridges between cage vertices and molybdenum. Treatment of these species with PEt3 in refluxing THF leads to displacement of a carbonyl ligand rather than an amino bridge.

Amine–nitrile coupling in amino-monocarbollide complexes of molybdenum

The Mo0 molybdenacarbaborane trianion [1-NH2-2,2,2-(CO)3-closo-2,1-MoCB10H10]3− is formed in situ from the reaction between [7-NH2-nido-7-CB10H10]3− and [Mo(CO)4{NH(CH2)5}2] in THF solution (THF = tetrahydrofuran). In the absence of nitriles, oxidation of this trianion by CH2CHCH2Br gives the MoII complex [1,2-μ-NH2-2,2,2-(CO)3-closo-2,1-MoCB10H10]−, isolated as its [N(PPh3)2]+ salt. However, in the presence of nitriles NCR, the same oxidation ultimately affords the species [N(PPh3)2][1,2-μ-{NHC(R)NH}-2,2,2-(CO)3-closo-2,1-MoCB10H10] in which amidine groups form a bridge between the carbon atom of the cage and the molybdenum, as a consequence of coupling of the nitrile with the cage-bound NH2 group. The acetamidine product [N(PPh3)2][1,2-μ-{NHC(Me)NH}-2,2,2-(CO)3-closo-2,1-MoCB10H10] is also formed by reaction of [7-NH2-nido-7-CB10H12]− with [Mo(CO)6] in refluxing NCMe, and its structure was confirmed by an X-ray diffraction study. Further oxidation of this species by I2 in the presence of CNBut gives the MoIV derivatives [1,2-μ-{NHC(Me)NH}-2,2-(CNBut)2-2-L-2-I-closo-2,1-MoCB10H10] (L = CO, CNBut), of which the tris(isocyanide) complex has been studied by X-ray diffraction.

The seventeen- and eighteen-electron metallacarbaboranes [1,1,1-(CO)3-2-Ph-closo-1,2-MnCB9H9]n−(n= 1, 2): a structurally characterized, redox-related pair

An eleven-vertex manganese-monocarbaborane dianion, upon one-electron oxidation, gives a stable radical monoanion in which the unpaired electron is delocalized over the cluster.

Alkyne coupling in rhenacarbaborane chemistry. Structure of [1,2-μ-NHBut-2,2-(CO)2-3,2-σ:η2-{C(CHBut)–CHCHBut}-closo-2,1-ReCB10H9]

The butadienyl moiety in the title compound is bound to both cage-boron and rhenium vertices, and arises from coupling of two alkyne molecules at the rhenium centre, unprecedented in metallacarbaborane chemistry.