Homoleptic Divalent Dialkyl Lanthanide-Catalyzed Cross-Dehydrocoupling of Silanes and Amines

Abstract

The rare-earth bis(alkyl) compound Sm{C-(SiHMe 2 ) 3 } 2 THF 2 (1b) is prepared by the reaction of samarium(II) iodide and 2 equiv of KC(SiHMe 2 ) 3 . This synthesis is similar to that of previously reported Yb{C-(SiHMe 2 ) 3 } 2 THF 2 (1a), and compounds 1a,b are isostructural. Reactions of 1b and 1 or 2 equiv of B(C 6 F 5 ) 3 afford SmC(SiHMe 2 ) 3 HB(C 6 F 5 ) 3 THF 2 (2b) or Sm{HB-(C 6 F 5 ) 3 } 2 THF 2 (3b), respectively, and 1,3-disilacyclobutane {Me 2 Si-C(SiHMe 2 ) 2 } 2 as a byproduct. Bands from 2300 to 2400 cm −1 assigned to ν BH in the IR spectra and highly paramagnetically shifted signals in the 11 B NMR spectra of 2b and 3b provided evidence for Sm-coordinated HB(C 6 F 5 ) 3 . Compounds 1a,b react with the bulky N-heterocyclic carbene (NHC) 1,3-di-tert-butylimidazol-2-ylidene (ImtBu) to displace both THF ligands and give three-coordinate monoadducts Ln{C-(SiHMe 2 ) 3 } 2 ImtBu (Ln = Yb (4a), Sm (4b)). Complexes 4a,b catalyze cross-dehydrocoupling of organosilanes with primary and secondary amines at room temperature to give silazanes and H 2 , whereas 1a,b are not effective catalysts under these conditions. Second-order plots of ln{[Et 2 NH]/[Ph 2 SiH 2 ]} vs time for 4a-catalyzed dehydrocoupling are linear and indicate first-order dependences on silane and amine concentrations. However, changes in the experimental rate law with increased silane concentration or decreased amine concentration reveal inhibition by silane. In addition, excess ImtBu or THF inhibit the reaction rate. These data, along with the structures of 4a,b, suggest that the bulky carbene favors low coordination numbers, which is important for accessing the catalytically active species.

Antimony-ligated dysprosium single-molecule magnets as catalysts for stibine dehydrocoupling

“…A recent study has shown that divalent rare earth alkyl complexes are effective catalysts for the cross-dehydrocoupling of silanes and amines to give silazanes. 47 …”

Silicon–Nitrogen Bond Formation via Heterodehydrocoupling and Catalytic N‐Silylation

“…Sadow and co‐workers synthesized samarium and ytterbium dialkyl complexes bearing NHC ligands, and good conversions were afforded by both compounds with primary and secondary silanes [53] . An experimental ternary rate law precluded the formation of M‐SiR 3 intermediates, and a coordinately unsaturated M‐NR 2 species was hypothesized to lead to Si−N bond formation.…”

Half‐Sandwich Alkyl, Amido, and Iodo Samarium(II) Complexes: Non‐Conventional Sterically Governed Oxidation of (tBu4Carb)2Sm

“…As a general rule, bulky hydrocarbyl ligands that lack β‐hydrogen atoms ([C(SiMe 3 ) 3 ],– [C(SiMe 3 ) 2 (SiMe 2 CH=CH 2 )]) or contain Lewis base groups able to coordinate to the metal center ([C(SiMe 3 ) 2 (SiMe 2 OMe)], [Me 3 SiCH(C 6 H 4 )NMe 2 ], bis(phosphinimino)methanide) are used for this purpose. Sadow and co‐workers proposed an original way of stabilization of Ln II bis(alkyl) species via β‐SiH agostic interactions between Ln II and [C(SiHMe 2 ) 3 ] ligands . It is worth noting that mixed‐ligand Ln II alkyl species coordinated by supporting ligand are even more rare than homoleptic ones.…”