Occurrence Of Neighboring Group Participation Reactions In Amide-N And Amidine Complexes Derived From Pentaammine(Dinitrile)Cobalt(Iii) Ions

N-Bonded pentaamminecobalt(III) complexes of 2-cyanobenzamide, 2-cyanoacetamide, and fumaric, succinic, glutaric, and adipic amide-nitriles have been prepared. The kinetics of the base hydrolysis of (succinonitrile)pentaamminecobalt(III) have been measured: k(obsd) = k(OH) [OH-]; k(OH) = 1.23 x 10(3) {I = 1.00 M (NaCH3COO), 25 degrees C}. Amido-N-coordinated 2-cyanobenzamide cyclized in aqueous base, and it forms [(1-oxo-3-iminoisoindolino-endo-N)pentaamminecobalt(III). In aqueous acid it protonates on the exo-imine and solvolyzes (k(H) = 7.9 x 10(-5) s(-1)), forming the pentaammineaquacobalt(III) complex and 1-oxo-3-iminoisoindoline. In aqueous acid the amido-N complexes are protonated on the amide oxygen. The 2-cyanobenzamide species rearranges to form the nitrile-bonded linkage isomer in aqueous acid and also in Me(2)SO-d(6), while the succinic amide nitrile complex rearranges more slowly in aqueous acid to form solely the nitrile-bonded linkage isomer. The kinetics of the reaction were k(obsd) = f(k(H)[H+]/(K-a + [H+])) where k(H) = 3.4 x 10(-4) M(-1) s(-1) and K-a = 6.76 x 10(-2) M, pK(a) 1.2; pK(a) 1.3 (spectrophotometric) {I = 1.00 M (LiClO4 . 3H(2)O), 25 degrees C}. In Me(2)SO-d(6) this amide-N complex reacts by three pathways: solvolysis, amide-hr to -O isomerization, and amide-N to nitrile-bonded rearrangement (10%)/. The conjugate acid of the 2-cyanoacetamido-N complex reacted in both aqueous acid and acidified Me(2)SO-d(6) by solvolysis, amide N to O isomerization, and amide-hr to nitrile-bonded rearrangement (17% in each solvent), The fumaric, glutaric, and adipic amide-nitrile complexes bonded through the amide nitrogen react only by solvolysis and amide-N to -O isomerization. Pentaamminecobalt(III) complexes of 2-cyanobenzamidine and succinic, glutaric, and adipic amidine-nitriles bonded through the amidine secondary nitrogen have been prepared. The 2-cyanobenzamidine complex undergoes rapid ligand cyclization to form the corresponding complex of 1,3-diiminoisoindoline bonded through the deprotonated endocyclic nitrogen. In aqueous acid the complex is protonated on one of the exo-imines, and this solvolyzes to form the pentaammineaquacobalt(III) complex and 1,3-diiminoisoindoline (k(H) = 1.7 x 10(-3) s(-1) (0.5 M HCl, 25 degrees C). Coordinated succinic amidine-nitrile also cyclizes in liquid ammonia to yield the complex of 2,5-diiminopyrrolidine bonded through the deprotonated endocyclic nitrogen. This is stable in aqueous base but solvolyzes rapidly (t(1/2) (s)) in aqueous acid to the aqua complex and succinimide; the latter is formed by hydrolysis of the free 2,5-diiminopyrrolidine. The dinuclear complex mu-decaammine(succinonitrile)dicobalt(III) was synthesized; in aqueous base it forms mu-(succinamido-N)-decaamminecobalt(III). The dinuclear dinitrile complex reacts in liquid ammonia to form the corresponding succinic amidine-nitrile species which cyclizes rapidly to form mu-decaammine(2,5-diiminopyrrolidino)cobalt(III) in which the ligand is bonded to cobalt(III) through the exo-imines.