New Titanium Complexes and Their Use in Hydroamination and Hydroaminoalkylation Reactions

Abstract

The synthesis of three new sterically crowded titanium complexes which all possess an identical formamidinato ligand, two dimethylamido ligands and in addition, a 2‐aminopyridinato ligand that contains either an N‐methyl, an N‐phenyl, or an N‐cyclohexyl substituent is presented. All new complexes are easily accessible from a common titanium mono(formamidinate) precursor and correspondingly N‐substituted 2‐aminopyridines. Furthermore, the new complexes are used as catalysts for selected hydroamination and hydroaminoalkylation reactions and finally, the catalytic performance of the new catalysts is compared with the performance of the titanium mono(formamidinate) precursor.

Ureate Titanium Catalysts for Hydroaminoalkylation: Using Ligand Design to Increase Reactivity and Utility

“…With a TOF of 11 h –1 , our monoligated ureate ligand L7 /Ti­(NMe 2 ) 4 ( Ti1 ) system demonstrates excellent activity for this specific reaction with unactivated substrates and compares favorably to other titanium catalysts based on commercially available Ti­(NMe 2 ) 4 ( Ti1 ). Furthermore, there is no indication of interference of the liberated dimethylamine in the hydroaminoalkylation process, which has been observed in other systems ( vide infra ). ,,, …”

“…For the reaction of 1-octene (Table , entry 1) quantitative yields with excellent regioselectivities for the branched product are achieved within 2 h, which is considerably faster than those of other reported easily assembled titanium catalysts based on Ti­(NMe 2 ) 4 ( Ti1 ), ,,, and approaches the reactivity of the corresponding acyclic ureate tantalum catalysts. , Interestingly, for the in situ system of Ti1 and L7 , catalyst loadings can be reduced to 1% for this specific reaction with 1-octene; however, the reaction times increase to 72 h to obtain a quantitative yield.…”

“…Furthermore, there is no indication of interference of the liberated dimethylamine in the hydroaminoalkylation process, which has been observed in other systems (vide infra). 41,42,45,61 We were interested in a direct comparison of the L7/Ti1 in situ system to the preisolated titanium catalyst. However, even when the temperature was lowered to −30 °C and addition of the ligand to a very dilute solution of Ti(NMe 2 ) 4 (Ti1) was slow, only a mixture of mono-and bis-ligated titanium ureate complexes could be isolated.…”

Hydroaminoalkylation for the Catalytic Addition of Amines to Alkenes or Alkynes: Diverse Mechanisms Enable Diverse Substrate Scope

“…Attempts to use mixed formamidinate and aminopyridinate ligated precatalysts (Figure 4, 2019) showed no improvements for reactivity or regioselectivity as compared with the complex highlighted in Scheme 10. 72 The simple N,N-chelate framework is readily modified to improve reactivity. Scheme 11 shows a bulky proligand that is reacted in situ with TiBn 4 to generate a very reactive catalyst that can accomplish neat and rapid reactions, in as little as 2 min.…”

“…A series of N,N -chelating Ti hydroaminoalkylation catalysts developed by the Doye group to improve substrate scope and modify regioselectivity. ,,− …”