Synthesis of chelating bidentate and tridentate cyano ligands and their complexes with Group VII metal carbonyls

Two new bidentate cyano ligands, DiCN-3 (2) and DEN-4 (3) (a,w-bis(2-cyanophenoxy)propane and butane, respectively), have been prepared. These ligands and the ethane analogue DEN-2 (1) react with Mn(C0)5Br to afford complexes of the composition Mr~(cO)~(DicN-n)Br (n= 2, 9; n = 3, 10; n = 4, 11). Complexes 9 and 10 appear to be mononuclear and contain 13and 14-membered chelate rings, respectively. Ligand 3 in 11 might be either chelated or bridged. IR studies of the reaction between 1-3 and Mn2(C0)6(CH&N)2(p-Br)2 show that, under identical conditions, more nitrile groups of 1 than of 2 and 3 are bound to the Mn(C0)3Br unit; this results suggests that DiCN-2 is a better chelating ligand than DiCN-3 or DiCN-4. A novel tricyano ligand, TriCN (1,3,5-tris(2-cyanophenyl)benzene (8)) has been synthesized from 2methylacetophenone. TriCN functions either as a bidentate ligand, as in M(CO)3(TriCN)Br (M = Mn, 12; M = Re, 14), or as a tridentate ligand, as in [M(CO),(TriCN)]PF6 (M = Mn, 13; M = Re, IS). Complexes 13 and 15 of TriCN are the first examples in which a tridentate cyano ligand chelates to a single metal center through its nitrogen lone pairs.