Author : Aaron Patrick Walsh
Publisher :
ISBN 13 :
Total Pages : 391 pages
Book Rating : 4.:/5 (93 download)
Book Synopsis Transition Metal-mediated Carbon-heteroatom Bond Activation by : Aaron Patrick Walsh
Download or read book Transition Metal-mediated Carbon-heteroatom Bond Activation written by Aaron Patrick Walsh and published by . This book was released on 2015 with total page 391 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Two transition metal-mediated systems were studied to understand6 the dominant and fundamental factors involved in controlling the reactivity of activation of relatively strong carbon-heteroatom bonds. The metal arene dimeric complex, [Cp*RhCl2]2, was used to facilitate ortho-directed carbon-hydrogen bond activation with the assistance of the exogenous organic base sodium acetate and derivatives thereof to explore the influence of pKa on the concerted metalation-deprotonation pathway and the implications the effect has in the overall cyclometalation of the substrate. In general, the cyclometalation of 2-(4-methoxyphenyl)pyridine by [Cp*RhCl2]2 is affected by two characteristics of the carboxylate additive: the pKa and steric bulk. In this study we sought to explore the ability of [Cp*RhCl2]2, and similar species, such as [Cp*IrCl2]2 and [(p-cymene)RuCl2]2, to activate carbon-hydrogen bonds of ortho-alkylated aromatic isocyanides by electrophilic means via the concerted metalation-deprotonation pathway. Eighteen new electrophilic metal-isocyanide complexes were synthesized and fully characterized. Isocyanide induced cleavage of the dimer, [LMCl2]2 {LM = Cp*Ir, Cp*Rh, or (p-cymene)Ru}, with 2,6-xylylisocyanide or 2,6-diethylphenylisocyanide produced complexes of the general formula LM(CNAr)Cl2. Halide metathesis of the dichloride complexes with sodium iodide produced the corresponding complexes with the general formula LM(CNAr)I2. For the analogous ruthenium complexes better results were achieved via isocyanide induced cleavage of [(p-cymene)RuI2]2. From these neutral complexes, reaction with AgPF6 in acetonitrile gave cationic, solvent-coordinated complexes that are chiral-at-metal. They have been fully characterized and crystallize as racemates. Reactions with rhodium gave either the previously unreported [Cp*RhCl(MeCN)]2[(PF6)2] when starting from Cp*Rh(CNAr)Cl2, or [Cp*Rh(MeCN)3][(PF6)2] and Cp*Rh(CNAr)I2 when starting from Cp*Rh(CNAr)I2. Several bases were probed to see if C-H activation at a benzylic position to create a novel metallacycle could be induced, but were not successful in any case. The other system studied the reactivity of the {(dippe)Pt0} (dippe = (iPr)2PCH2CH2P(iPr)2) fragment with carbon-chalcogenide bonds and mechanistic pathways that could be involved in cleaving these bonds and subsequent reactions that occur to account for the observed products. The precursor complex, (dippe)Pt(NBE)2 (NBE = norbornene), oxidatively adds both carbon-sulfur and carbon-oxygen bonds. In the case of carbon-sulfur bond activation the platinum fragment reacts with cyclic and linear thioethers, upon heating, to give oxidative addition products. Further heating leads to disproportionation and concomitant formation of desulfurized organic by-products and platinum-bisthiolate complexes, (dippe)Pt(SR)2, in several cases. Furthermore, the platinum fragment also oxidatively adds a variety of esters upon heating in which the less reactive, ether carbon-oxygen bond is cleaved to yield alkyl-, and aryl-platinum carboxylates, (dippe)Pt(OCOR)2. Further heating, again, leads to disproportionation and concomitant formation of deoxygenated organic by-products and platinum-biscarboxylate."--Pages vii-viii.
