Design, Synthesis, and Chemistry of Bis(σ)borate and Agostic Complexes of Group 7 Metals

Abstract

A series of new bis(σ)borate and agostic complexes of group 7 metals have been synthesized and structurally characterized from various borate ligands, such as trihydrobis(benzothiazol-2-yl)amideborate (Na[(H₃ B)bbza]), trihydro(2-aminobenzothiazolyl)borate (Na[(H₃ B)abz]), and dihydrobis(2-mercaptopyridyl)borate (Na[(H₂ B)mp₂ ]) (bbza=bis(benzothiazol-2-yl)amine, abz=2-aminobenzothiazolyl, and mp=2-mercaptopyridyl). Photolysis of [Mn₂ (CO)₁₀ ] with Na[(H₃ B)bbza] formed bis(σ)borate complex [Mn(CO)₃ (μ-H)₂ BHNCSC₆ H₄ (NR)] (1; R=NCSC₆ H₄ ). Octahedral complex [Re(CO)₂ (N₃ C₂ S₂ C₁₂ H₈ )₂ ] (2) was generated under similar reaction conditions with [Re₂ (CO)₁₀ ]. Similarly, when [Mn₂ (CO)₁₀ ] was treated with Na[(H₃ B)abz], bis(σ)borate complex [Mn(CO)₃ (μ-H)₂ BH(HN₂ CSC₆ H₄ )] (3) and the agostic complex [Mn(CO)₃ (μ-H)BH(HN₂ CSC₆ H₄ )₂ ] (4) were formed. To probe the potential formation of agostic complexes of the heavier group 7 metals, we carried out the photolysis of [M₂ (CO)₁₀ ] with Na[(H₂ B)mp₂ ] and found that [M(CO)₃ (μ-H)BH(C₅ H₄ NS)₂ ] (5: M=Re; 6: M=Mn) was formed in moderate yield. Complexes 1 and 3 feature a (κ³ -H,H,N) coordination mode, whereas 4, 5, and 6 display both (κ³ -H,N,N) and (κ³ -H,S,S) modes of the corresponding ligands. To investigate the lability of the CO ligands of 1 and 3, we treated the complexes with phosphine ligands that generated novel bis(σ)borate complexes [Mn(μ-H)₂ (BHNCSC₆ H₄ )(NR)(CO)₂ PL₂ L'] (R=NCSC₆ H₄ ; 7 a: L=L'=Ph; 7 b: L=Ph, L'=Me) and [Mn(μ-H)₂ BHN(NCSC₆ H₄ )R(CO)₂ PL₂ L'] (R=NCSC₆ H₄ ; 8 a: L=L'=Ph; 8 b: L=Ph, L'=Me). Complexes 7 and 8 are structural isomers with different coordination modes of the bbza ligand. In addition, DFT calculations were performed to shed some light on the bonding and electronic structures of these complexes.