The first silyl- and germylboryl complexes: synthesis from novel (dichloro)silyl- and (dichloro)germylboranes, structure and reactivity

Abstract

A series of silyl- and germyl(dichloro)boranes Cl₂B–ER₃ (5, ER₃ = Si(SiMe₃)₃; 6, ER₃ = Ge(SiMe₃)₃; 7, ER₃ = Si(SiMe₃)₂–Si(SiMe₃)₃; 8, ER₃ = SiPh₃) was obtained in good yields from the corresponding bis(dimethylamino)boranes (Me₂N)₂B–ER₃ (1, ER₃ = Si(SiMe₃)₃; 2, ER₃ = Ge(SiMe₃)₃; 3, ER₃ = Si(SiMe₃)₂–Si(SiMe₃)₃; 4, ER₃ = SiPh₃) upon reaction with BCl₃, and fully characterised in solution. These compounds proved to be versatile starting materials for the synthesis of the first silyl- and germylboryl complexes by salt elimination reactions starting from anionic transition metal complexes of the type Na[(η⁵-C₅R₅)Fe(CO)₂] and K[(η⁵-C₅R₅)Mn(H)(CO)₂]. The novel iron and manganese boryl complexes [(η⁵-C₅R₄R′)(OC)₂Fe–B(Cl)Si(SiMe₃)₃] (9a, R = R′ = H; 9b, R = H, R′ = Me; 9c, R = R′ = Me), [(η⁵-C₅H₅)(OC)₂Fe–B(Cl)Ge(SiMe₃)₃] (9d), [(η⁵-C₅H₅)(OC)₂Fe–B(Cl)Si(SiMe₃)₂Si(SiMe₃)₃] (9e), [(η⁵-C₅H₄Me)(OC)₂(H)Mn–B(Cl)Si(SiMe₃)₃] (10a) and [(η⁵-C₅H₄Me)(OC)₂(H)Mn–B(Cl)Ge(SiMe₃)₃] (10b) were obtained in yields between 35 and 70%, fully characterised in solution and in the case of 9a, d, and 10a also in the crystalline state. They are all characterised by metal–boron σ-bonds without indication of any metal-to-boron π-backdonation. There is, however, spectroscopical and structural evidence for the presence of a Mn–H–B bridge in the case of the manganese complexes 10a, b. The first transhalogenation of a metal coordinated boryl ligand was achieved by reaction of 9a with TlF affording the fluoroboryl complex [(η⁵-C₅H₅)(OC)₂Fe–B(F)Si(SiMe₃)₃] (11), which was characterised in solution and in the solid state.