Cooperative B-H bond activation: dual site borane activation by redox active κ 2 - N , S -chelated complexes.

Cooperative dual site activation of boranes by redox-active 1,3- N , S -chelated ruthenium species, mer -[PR 3 {κ 2 - N , S -(L)} 2 Ru{κ 1 - S -(L)}], ( mer -2a: R = Cy, mer -2b: R = Ph; L = NC 7 H 4 S 2 ), generated from the aerial oxidation of borate complexes, [PR 3 {κ 2 - N , S -(L)}Ru{κ 3 - H , S , S '-BH 2 (L) 2 }] ( trans - mer -1a: R = Cy, trans - mer -1b: R = Ph; L = NC 7 H 4 S 2 ), has been investigated. Utilizing the rich electronic behaviour of these 1,3- N , S -chelated ruthenium species, we have established that a combination of redox-active ligands and metal-ligand cooperativity has a big influence on the multisite borane activation. For example, treatment of mer -2a-b with BH 3 ·THF led to the isolation of fac -[PR 3 Ru{κ 3 - H , S , S '-(NH 2 BSBH 2 N)(S 2 C 7 H 4 ) 2 }] ( fac -3a: R = Cy and fac -3b: R = Ph) that captured boranes at both sites of the κ 2 - N , S -chelated ruthenacycles. The core structure of fac -3a and fac -3b consists of two five-membered ruthenacycles [RuBNCS] which are fused by one butterfly moiety [RuB 2 S]. Analogous fac -3c, [PPh 3 Ru{κ 3 - H , S , S '-(NH 2 BSBH 2 N)(SC 5 H 4 ) 2 }], can also be synthesized from the reaction of BH 3 ·THF with [PPh 3 {κ 2 - N , S -(SNC 5 H 4 )}{κ 3 - H , S , S '-BH 2 (SNH 4 C 5 ) 2 }Ru], cis - fac -1c. In stark contrast, when mer -2b was treated with BH 2 Mes (Mes = 2,4,6-trimethyl phenyl) it led to the formation of trans - and cis -bis(dihydroborate) complexes [{κ 3 - S , H , H -(NH 2 BMes)Ru(S 2 C 7 H 4 )} 2 ], ( trans -4 and cis -4). Both the complexes have two five-membered [Ru-(H) 2 -B-NCS] ruthenacycles with κ 2 -H-H coordination modes. Density functional theory (DFT) calculations suggest that the activation of boranes across the dual Ru-N site is more facile than the Ru-S one.