Cyclopentadiene Biphenyl Side Chain Bridge And Imidazole And Its Fourth Subgroup Metal Complexes Synthesis, Characterization And Catalytic Activity Of Study

The so-called Constrained Geometry Complexes (CGCs) since their introduction into the organometallic chemistry in1991have been attracted a great deal of attention of research teams around the world. CGCs, once proved to be potent catalysts for olefin polymerization, were extensively investigated during the last several decades. Beyond their application in polymerization reactions, the catalytic activity of CGCs in various other transformations was also tested, and in recent years the number of works in this area increases rapidly. The review part of the dissertation describes the known synthetic approaches to CGCs along with their applications in catalysis.The Result and Discussion section of the present work comprises several parts. The first part reports the development of a synthetic approach to new ligands (5a-f) in which cyclopentadienyl and benzimidazol-2-yl moieties are linked by either a C1or C2bridge [-CMe2-(5a),-CHPh-(5b),-CPh2-(5c),-CMe2CH2-(5d),-CHPhCH2-(5e),-CPh2CH2-(5f)] starting from available6-phenyl-,6,6-diphenyl-, and6,6-dimethylfulvenes and two lithiated N-CH(OEt)2protected benzimidazoles [2-methyl substituted (2b) or parent (2a) ones]. While, unfortunately, preparation of5b and5c failed due to unavoidable reasons, other ligands of interest could be isolated in moderate or good yields. The known CH-acidity of the methyl group hydrogens in6,6-dimethylfulvene also presented a noticeable problem and lowered the yields of5a and5d. In addition, we unexpectedly observed an N-ethylation of5f·HCl during its re-crystallization from hot ethanol which afforded the correspondent benzimidazolium salt5f’in a high yield.Reaction of compounds5a,5e, and5f with the Group4metal tetrakis-amides [(Et2N)4Ti or (Et2N)4Zr] yielded the target CGCs [M=Ti, bridges:-CMe2-(6a),-CHPhCH2-(6b),-CPh2CH2-(6d); M=Zr, bridges:-CHPhCH2-(6c),-CPh2CH2-(6e)].When examining the reactivity of the mentioned complexes, we, somewhat serendipitously, found out their ability to catalyze the dehydrocoupling reaction between primary or secondary amines and sterically non-hindered primary or secondary silanes. Remarkably, it is the first time when such a feature has ever been observed for CGCs.Complexes6c,6e exhibit relatively high activity towards the cross coupling reaction in Et2NH/PhSiH3,t-BuNH2/PhSiH3and n-BuNH2/PhSiH3systems. Addition of tris(perfluorophenyl)borane (BCF) dramatically promotes this reactions. Meanwhile, complexes6b and6d were proved to be inactive under the similar reaction conditions (or demonstrated only negligible activity) even in the presence of BCF. In case of6e, presence of large excess of t-butylamine in C6D6caused its transamination which afforded complex6f. In the Discussion section of the work, possible mechanistic pathways of the dehydrocoupling reaction catalyzed by CGCs are also considered.Besides catalyzing the dehydrocoupling reaction, complex6e exhibits certain activity in CO2fixation and olefin polymerization. Its formal1:1N-adduct with BCF (6j) is capable to effectively fix CO2that yields an individual crystalline product. Unfortunately, X-ray structural investigation of this material failed due to decomposition of the resulting product. The olefin polymerization activity of6e activated by either MAO or BCF is rather moderate (1×103g·mol-1·MPa-1·h-1). Attempts to catalyze reactions between acetonitrile or pyridine and phenylsilane with6e failed.Additionally to the mainstream of the research, a synthetic approach to another type of cyclopentadienyl-type ligands with a pendant imino-group has been explored and two representatives of this family of compounds, namely C5H5-CH=NBu-n (7a) and C5H5-CH=NBu-t (7b)(the latter isolated and characterized in its lithiated form as a1:1solvate with THF), were prepared. An interesting cluster-type product of a regulated partial hydrolysis of C5Me5ZrCl3(7c) of has been also described.Structures of all organic and organometallic compounds under consideration have been adequately confirmed by’H and13C{1H} NMR spectroscopy and/or GC-MS method. Crystal and molecular structures of5f",6a,6b,6c,6d,6e,6f,6g,7b, and7c have been established by X-ray diffraction analysis.