B-P Coupling: Metal Stabilized Phosphinoborate Complexes

In an effort to establish B-P coupling reactions without the use of phosphine-borane dehydrocoupling agent, we have developed a new synthetic methodology employing group 8 metal σ-borate complex [{κ³ -H,S,S'-BH₂ L₂ }Ru{κ³ -H,H,S-BH₃ L}] (L=NC₅ H₄ S), 1. Treatment of 1 with chlorodiphenyl phosphine (PPh₂ Cl) yielded 1,5-P,S chelated Ru-dihydridoborate species [PPh₂ H{κ³ -H,H,S-BH(OH)L}Ru{κ² -P,S-(Ph₂ P)BH₂ L}], 2. The insertion of phosphine moiety (PPh₂ ) by the cleavage of 3c-2e σ(Ru^… H-B) bonding interaction led to the formation of B-P bond. The κ² -P,S chelated six-membered ring adopted a boat conformation in complex 2. The heterocycle is made of all different atoms, which is one of the rarest examples of heteroatomic ring systems. Theoretical outcomes demonstrated the electronic insight of B-P coupling and stabilization through transition metal. In order to explore an alternate route of B-P bond formation, we have further explored the reaction of 1 and Ru-bis(dihydridoborate) complex, 5 with secondary phosphine oxide (SPO). Although, thermolysis of 1 with diphenylphosphine oxide yielded analogous σ-borate complex 3, the similar reaction of 5 at room temperature led to the formation of novel phosphinous(III) acid incorporated Ru(σ-borate)(dihydridoborate) complex, 6. In a similar fashion, the reaction of 5 with phosphite ligand generated Ru(σ-borate)(dihydridoborate) complex, 7, which is analogous to 6.