Cobalt-Mediated Selective B−H Activation and Formation of a Co−B Bond in the Reaction of the 16-Electron CpCo Half-Sandwich Complex Containing an o-Carborane-1,2-dithiolate Ligand with Ethyl Diazoacetate

Reactivity Modes of Cp*M-Type Half-Sandwich Dichalcogenolate Complexes with 2,6-Disubstituted Aryl Azides: The Effects of the Metal Center, Chalcogen, and Ligand Moiety on Product Formation

Cp*M-type half-sandwich dichalcogenolate complexes bearing either carborane or benzene moieties show diverse reactivity patterns toward two selected 2,6-disubstituted aryl azides under thermal or photolytic conditions. The chalcogen (S and Se) has little effect on the formation of final products. However, the effects of both the metal center and the ligand moiety of the metal precursor on the reactions were significant. Compared to iridium precursor Cp*IrS₂C₂B₁₀H₁₀ (1a), rhodium and cobalt analogues (1b: Cp*RhS₂C₂B₁₀H₁₀, 1c: Cp*CoS₂C₂B₁₀H₁₀) demonstrated no reactivity toward aryl azides. The reaction of Cp*IrSe₂C₂B₁₀H₁₀ (1d) with 2,6-Me₂C₆H₃N₃ led to the clean formation of complex 2 with C(sp³)-H activation of one methyl group of the Cp* ligand and loss of N₂ along with the rearrangement of the benzene ring of the original azide ligand, whereas the treatment of Cp*IrS₂C₆H₄ (1e) with 2,6-Me₂C₆H₃N₃ under the same reaction conditions gave a 16-electron half-sandwich complex 5 featuring C-N coupling on one methyl group from the Cp* ligand. When 2-Me-6-NO₂C₆H₃N₃ was employed, the same reaction patterns for forming products (3 and 6) with the nitro group migrating to the para-position versus the original aryl azide were observed. In addition, the reaction with metal precursor 1d generated another product 4 featuring the exchange of nitro and azido groups, while the reaction with 1e afforded another complex 7 with the formation of the N-NO₂ moiety. All new complexes were characterized by spectroscopy methods, and single-crystal X-ray analyses were performed for complexes 2 and 5-7. Furthermore, radical mechanisms for the formation of complexes 2-7 were proposed.

Efficient synthesis of carborane azo derivatives and their reactivity

An iridium(iii)-catalyzed C–N-bond-forming direct synthesis of carborane azo derivatives was developed.

Novel inorganic heterocycles from dimetalated carboranylamidinates

Mono- and dianionic carboranylamidinates are readily available in one-pot reactions directly from o-carborane (1). In situ-monolithiation of 1 followed by treatment with N,N'-diisopropylcarbodiimide, (i)PrN=C=N(i)Pr, or N,N'-dicyclohexylcarbodiimide, CyN=C=NCy, provided the lithium carboranylamidinates (o-C2B10H10C(NH(i)Pr)(=N(i)Pr)-κ(2)C,N)Li(DME) (2a) and (o-C2B10H10C(NH(i)Cy)(=N(i)Cy)-κ(2)C,N)Li(THF)2 (2b). Controlled hydrolysis of 2a,b afforded the free carboranylamidines o-C2B10H11C(NH(i)R)(=N(i)R) (3a: R = (i)Pr, 3b: R = Cy). The first dimetalated carboranylamidinates, o-C2B10H10C(N(i)Pr)(=N(i)Pr)Li2(DME)2 (4a) (DME = 1,2-dimethoxyethane) and o-C2B10H10C(N(i)Pr)(=N(i)Pr)Li2(THF)4 (4b), were prepared in high yield (83% yield) directly from 1 using a simple one-pot synthetic protocol. Treatment of 4b with 2 equiv. of Me3SiCl afforded the disilylated derivative o-C2B10H10-κ(2)C,N-[C(N(i)PrSiMe3)(=N(i)Pr)]SiMe3 (5). Dianionic 4b also served as an excellent precursor for novel inorganic heterocycles incorporating the closo-1,2-C2B10H10 cage, including the unsymmetrical distannene [o-C2B10H10C(N(i)Pr)(=N(i)Pr)-κ(2)C,N]Sn=Sn[((i)PrN)2C(n)Bu]2 (6) and the azaphosphole derivative [o-C2B10H10C(N(i)Pr)(=N(i)Pr)-κ(2)C,N]PPh (7). Surprisingly, it was found that the synthesis of new inorganic ring systems from dianionic carboranylamidinates can also be achieved by employing only 1 equiv. of n-butyllithium in the generation of the anionic carboranylamidinate intermediates. Using this straightforward one-pot synthetic protocol, the Group 14 metallacycles [o-C2B10H10C(NCy)(=NCy)-κ(2)C,N]SiR2 (R = Cl (8), Me (9), Ph (10)) and [o-C2B10H10C(NCy)([=NCy)-κ(2)C,N]GeCl2 (11) have become accessible. The same synthetic strategy could be successfully adapted to prepare the corresponding Group 4 metallocene derivatives Cp2Ti[o-C2B10H10C(NCy)(=NCy)-κ(2)C,N] (12) and Cp2Zr[o-C2B10H10C(NCy)(=NCy)-κ(2)C,N] (13). The molecular structures of 2b, 3b, 4b, 5, 6, 7, 10, 12, and 13 were confirmed by single-crystal X-ray diffraction.

Investigation into the reactivity of 16-electron complexes Cp#Co(S2C2B10H10) (Cp# = Cp, Cp*) towards methyl diazoacetate and toluenesulphonyl azide

A three-component reaction of the 16-electron half-sandwich complex Cp*Co(S₂C₂B₁₀H₁₀) (2) with both methyl diazoacetate (MDA) and toluenesulphonyl azide (TsN₃) led to the formation of complexes 3 and 4, while a two-component reaction of complex 2 with MDA afforded products 5–7.