Small molecule binding and activation on a cationic ruthenium center of a pincer complex

Abstract

Ruthenium pincer complex [RuHCl(PPh₃)(PNP)] (PNP = Me−N(CH₂CH₂PPh₂)₂) (1) was synthesized by reaction of RuHCl(PPh₃)₃ with Me-N(CH₂CH₂PPh₂)₂ and characterized. Abstraction of chloride ligand in complex 1 using NaBAr₄^f in the presence of small molecules such as N₂, H₂, O₂, and CO resulted in the formation of trans-[RuH(L)(PPh₃)(PNP)]BAr₄^f {L = N₂ (2), H₂ (4), O₂ (5), CO (6)} complexes. Complexes 2, 4, 5, and 6 have been characterized by various techniques. The reaction of [RuHCl(PPh₃)(PNP)] complex with NaBH₄ gave a borohydrido complex [RuH(η¹−BH₄)(PPh₃)(PNP)] (7) which upon reaction with NEt₃ generates a mixture of cis and trans dihydrides [RuH₂ (PPh₃)(PNP)] (8). The reaction of dihydride complexes with CO₂ leads to the formation of formate complex [RuH(η¹−HCO₂)(PPh₃)(PNP)] (9). In addition, dihydrogen complexes [Ru(η²-H²)(L)(PPh₃)(PNP)]ⁿ⁺ (L = Cl (10), CO (11)) having different trans donor ligands were synthesized by protonation of trans-[RuH(L)(PPh₃)(PNP)]ⁿ⁺ {n = 0, L = Cl; n = 1, L = CO} complexes with HOTf at low temperature. Complexes 1 and 6 have been characterized by X-ray crystallography.