Concurrent homolysis, β-elimination, and hydrolysis of macrocyclic alkylchromium complexes

The complexes L1(H2O)CrR2+ (L1=[14]aneN4) undergo homolytic chromiumcarbon bond cleavage in aqueous solutions (R=CHMe2, k=0.003 s−1; CH(Me)(Et), 0.013; CH(Et)2, 0.047) much more rapidly than the complexes in the aqua series, (H2O)5CrR2+. The hydrolysis, on the other hand, is much slower for the macrocyclic complexes. Both effects are discussed in terms of the steric congestion at the reaction site and the availability of coordinated molecules of water cis to the alkyl group. The complex L1(H2O)CrCH(CH3)2 2+ also undergoes β-elimination with a kinetic isotope effect of ∼1.7.