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

A series of new bis(sigma) borate and agostic complexes of group7 metals have been synthesized and structurally characterized from various borate ligands, such as trihydrobis( benzothiazol-2-yl) amideborate (Na[(H3B)bbza]), trihydro( 2-aminobenzothiazolyl) borate (Na[(H3B)abz]), and dihydrobis( 2-mercaptopyridyl) borate (Na[(H2B)mp(2)]) (bbza= bis(benzothiazol-2-yl) amine, abz=2-aminobenzothiazolyl, and mp=2-mercaptopyridyl). Photolysis of [Mn-2(CO)(10)] with Na[(H3B)bbza] formed bis(sigma) borate complex [Mn(CO)(3)(mu H)(2)BHNCSC6H4(NR)] (1; R= NCSC6H4). Octahedral complex [Re(CO)(2)(N3C2S2C12H8)(2)] (2) was generated under similar reaction conditions with [Re-2(CO)(10)]. Similarly, when [Mn-2(CO)(10)] was treated with Na[(H3B)abz], bis(sigma) borate complex [Mn(CO)(3)(mu-H)(2)BH(HN2CSC6H4)] (3) and the agostic complex [Mn(CO)(3)(mu-H)BH(HN2CSC6H4)(2) (4) were formed. To probe the potential formation of agostic complexes of the heavier group7 metals, we carried out the photolysis of [M-2(CO)(10)] with Na[(H2B)mp(2)] and found that [M(CO)(3)(mu-H) BH(C5H4NS)(2)] (5: M= Re; 6: M= Mn) was formed in moderate yield. Complexes 1 and 3 feature a (k(3)-H,H,N) coordination mode, whereas 4, 5, and 6 display both (k(3)-H,N,N) and (k(3)-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(s) borate complexes [Mn(mu-H)(2)(BHNCSC6H4)(NR)(CO)(2)PL2L'] (R= NCSC6H4; 7a: L= L'= Ph; 7b: L= Ph, L'= Me) and [Mn(mH) 2BHN(NCSC6H4) R(CO)(2)PL2L'] (R= NCSC6H4; 8a: L= L'= Ph; 8b: 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.