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.