Amido-imido niobium complexes with chloro-silyl- and amino-silyl-functionalized cyclopentadienyl ligands

The chloro-imido complex [Nb(eta(5)-C5H4-SiMe2Cl)(CH2Ph)Cl((NBu)-Bu-t)] undergoes selective substitution of the Nb-Cl bond when it is reacted with (LiNHBu)-Bu-t, giving [Nb(eta(5)-C5H4-SiMe2Cl)(CH2Ph)((NHBu)-Bu-t)((NBu)-Bu-t)], whereas preferential reaction at the Si-CI bond occurs with (NH2Bu)-Bu-t, giving [Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))(CH2Ph)Cl((NBu)-Bu-t)], which is then transformed into [Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))(CH2Ph)((NHBU)-B-t)] on further reaction with (NH2Bu)-Bu-t. Chemical reactivity studies demonstrate that a spontaneous transformation of [Nb(eta(5)-C5H4-SiMe2Cl)(CH2Ph)((NHBu)-Bu-t)((NBu)-Bu-t)] into [Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))(CH2Ph)Cl((NBu)-Bu-t)] takes place, via an intermolecular reaction, by attack of the silicon-bonded chlorine at the unsaturated niobium center. Benzylation of [Nb{eta(5)-C5H4-SiMe2((NHBu)-Bu-t)}(CH2Ph)Cl((NBu)-Bu-t)] with Mg(CH2Ph)(2). 2THF gives [Nb{eta(5)-C5H4-SiMe2((NHBu)-Bu-t)}(CH2Ph)(2)((NBu)-Bu-t)], which also results from reaction of the chloro-silyl derivative [Nb(eta(5)-C5H4-SiMe2Cl)(CH2Ph)(2)((NBu)-Bu-t)] with (NH2Bu)-Bu-t. The dichloro-imido complex [Nb(eta(5)-C5H4-SiMe2Cl)Cl-2((NBu)-Bu-t)], readily obtained from [Nb(eta(5)-C5H4-SiMe2Cl)Cl-4], also reacts preferentially at the Si-CI bond when treated with (NH2Bu)-Bu-t to give [Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))Cl-2((NBu)-Bu-t)], which is further transformed into [Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))Cl((NHBu)-Bu-t)((NBu)-Bu-t)]; the latter is alternatively prepared by reaction of [Nb(eta(5)-C5H4-SiMe2Cl)Cl-4] with a large excess of (NH2Bu)-Bu-t. The tetrachloro compound reacts with excess (LiNHBu)-Bu-t to give the constrained-geometry complex [Nb(eta(5)-C5H4-SiMe2(eta(1)-(NBu)-Bu-t))((NHBu)-Bu-t)((NBu)-Bu-t)], which is converted into the chloro-niobium derivative by reaction with SiMe3Cl. These constrained-geometry complexes may also be obtained from the dichloro derivative [Nb(eta(5)-C5H4-SiMe2Cl)Cl-2((NBu)-Bu-t)], by reaction with 3 or 2 equiv of (LiNHBu)-Bu-t, respectively, Thermal treatment of the benzyl compounds [Nb{eta(5)-C5H4-SiMe2((NHBu)-Bu-t)}(CH2Ph)X((NBu)-Bu-t)] (X = Cl, CH2Ph) at 160 degrees C results in formation of the silyl-amido complexes [Nb(eta(5)-C5H4-SiMe2(eta(1)-(NBu)-Bu-t))X((NBu)-Bu-t)] (X = Cl, CH2Ph) with elimination of toluene, whereas a similar transformation of the related iminoacyl complex [Nb{eta(5)-C5H4-SiMe2((NHBu)-Bu-t)}{eta(2)[C(CH2Ph){N(2,6-Me2C6H3)}](CH2Ph)((NBu)-Bu-t)] produces a simultaneous isomerization to give the vinylamido compound [Nb(eta(5)-C5H4-SiMe2(eta(1)-(NBu)-Bu-t))(N(CH=CHPh)(2,6-Me2C6H3))((NBu)-Bu-t)]. Insertion of CN(2,6-Me2C6H3) into the niobium-benzyl bonds of complexes [Nb{eta(5)-C5H4-SiMe2((NHBu)-Bu-t)}(CH2Ph)X((NBu)-Bu-t)] (X = Cl, CH2Ph) and [Nb(eta(5)-C5H4-SiMe2(eta(1)-(NBu)-Bu-t))(CH2Ph)((NBu)-Bu-t)] leads to the iminoacyl compounds [Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))(CH2Ph)((NBu)-Bu-t)] (X = Cl, CH2Ph) and Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))(eta(2)-[C(CH2Ph)(N(2,6-Me2C6H3))])((NBu)-Bu-t)], respectively. All of the reported new compounds were characterized by elemental analyses and H-1 and C-13 NMR spectroscopy, and the X-ray molecular structure of [Nb(eta(5)-C5H4-SiMe2((NHBu)-Bu-t))Cl-2((NBu)-Bu-t)] was studied by diffraction methods.