Metal-Induced B−H Bond Activation: Addition of Methyl Acetylene Monocarboxylate to CpCo Half-Sandwich Complexes Containing a Chelating 1,2-Dicarba-closo-dodecaborane-1,2-dichalcogenolate Ligand

Abstract

The reaction of the 16e half-sandwich complex {CpCo[S 2 C 2 B 10 H 10 ]} (1S) with methyl acetylene monocarboxylate at ambient temperature led to {CpCo[S 2 C 2 B 10 H 10 ] [CHC(CO 2 Me)CHC(CO 2 Me)]} (2S) and {CpCo[S 2 C 2 B 10 H 8 ][CHCH(CO 2 Me)] 2 } (3S). In2S the alkyne is 2-fold inserted into one of the Co-S bonds. 3S is a 16e B-disubstituted complex with the olefinic units in a Z/Z configuration. In comparison, {CpCo[Se 2 C 2 B 10 H 10 ]} (1Se) reacted with the alkyne to give rise to {CpCo[Se 2 C 2 B 10 H 10 ]-[CHC(CO 2 Me)CHC(CO 2 Me)]}(2Se),{CpCo[Se 2 C 2 B 10 H 9 ][CH 2 C(CO 2 Me)]}(4Se),and{CpCo[Se 2 C 2 B 10 H 8 ]-[CH 2 C(CO 2 Me)][CHCH(CO 2 Me)]} ( 5Se). 2Se is the analogue of 2S. Upon heating, 2S and 2Se catalyze cyclotrimerization of the alkyne to generate 1,3,5-and 1,2,4-tricarboxylatebenzenes. 4Se is an 18e B-substituted species with a B-CH 2 unit. 5Se is analogous to 4Se, but contains an olefinic substituent at the B(3)/B(6) site of the carborane in a Z configuration. Mechanistic implications on metal-induced B-H bond activation and catalytic cyclotrimerization of alkyne were elucidated. All new complexes were characterized by NMR spectroscopy ( 1 H, 11 B, 13 C), and X-ray structural analyses were reported for 2S, 2Se, 3S, 4Se, and 5Se.

Reactivity of a 16‐Electron CpCo Half‐Sandwich Complex Containing a Chelating 1,2‐Dicarba‐closo‐dodecaborane‐1,2‐diselenolate Ligand towards FcC(O)C≡CH

“…[6a,6b,7a,8a] Analogous structures and mechanistic studies have been reported by our group. [6][7][8] The reaction takes place through a series of sequential steps such as an alkyne insertion into a M-E (E = S, Se) bond, metal induced B-H activation, the formation of M-B, and then the formation of C-B. However, the reaction of 1 with FcC(O)CϵCH in MeOH at ambient temperature leads to 5 (Scheme 3, Figure 4).…”

“…The characteristic doublets at 3.19 and 1.25 ppm with J = 16 Hz are ascribed to the alkyl group of the B-CH 2 unit. [6,7a,7b,8a] In the 13 C NMR spectrum, two signals at 139.2 and 128.1 ppm are assigned to C (6) and C(7), respectively. The broad signal of C(3) at 29.7, C(4) at 106.1, and C(1)/C(2) at 62.9/59.4 ppm have been unquestionably designated and are in parallel with data observed for 4.…”

“…[2][3][4] Furthermore, the combination of the electron deficiency at the metal center and the reactive metal-chalcogen bonds renders these 16-electron species interesting candidates for reactions with alkynes. [5][6][7][8] Our previous studies on the reactivity of these 16-electron starting materials have shown that the metal center, the chalcogen, the substrate, and the ancillary ligand together with the reaction temperature, the solvent, and the ratio of the reactants play key roles in the types and structures of the products. [6][7][8] For instance, the reaction of CpCo(S 2 C 2 B 10 H 10 ) with PhCϵCH leads to two 18-electron products: the alkyne double-inserted product at the Co-S to an unexpected product, [{FcC(O)CHCH}CpCo-(Se 2 C 2 B 9 H 9 ){CH 2 CC(O)Fc}] (5), which contains two alkynes and a nido-C 2 B 9 cage.…”

Reactions of a 16-electron Cp*Co half-sandwich complex containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dithiolate ligand with alkynones HC≡C-C(O)R (R = OMe, Me, Ph)

“…For example, they are capable of combining with metal species to generate new types of metal-metal bonded complexes with one or two ortho-carborane-1,2-dichalcogenolate ligands [6][7][8][9][10][11], and Lewis bases-including biologically interesting substrates such as NH 3 , CO and diazenes-to generate their 18e congeners [14][15][16][17]. Furthermore, the combination of electron deficiency at the metal center and the reactivity of the metal-chalcogen bonds renders these complexes interesting candidates for reactions with unsaturated substrates such as alkynes [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35].…”

“…In addition, the reactions of the 16e complexes CpCo(E 2 C 2 B 10 H 10 ) (E = S, Se) with phenylacetylene and methyl acetylene monocarboxylate also led to Scheme 1 Some related compounds in the literature in which alkynes have been twofold inserted into Rh−S bonds [25][26][27][28][29][30][31].…”