Chromium(0) tricarbonyl complexes of 1,3,5-triazacyclohexanes

Abstract

Three 1,3,5-trialkyl-1,3,5-triazacyclohexane chromium tricarbonyl complexes fac-[Cr(CO) ₃ (C ₃ H ₆ N ₃ R ₃ )] (R = Me, Et or Bu ^t ) have been prepared and their reactivities investigated. Both the kinetic and the thermodynamic stabilities of the complexes increase as the size of the R group increases. When R = Me or Et, the ligand is susceptible to displacement to produce [Cr(CO) ₃ L ₃ ] [L = pyridine or P(OMe) ₃ ]. Room-temperature single crystal X-ray studies were carried out on the R = Me and Bu ^t complexes. Both molecules adopt the expected ‘piano-stool’ configuration with putative 3m symmetry; a crystallographic mirror plane passes through the methyl adduct. The Cr–N distances in the R = Me complex [2.153(3), 2 × 2.181(2) Å] are shorter than in the Bu ^t case [2.202(5) - 2.216(4) Å]; in both the substituents are obligate equatorial relative to the triazacyclohexane ring.