Spectroscopic studies of thermally activated C-F bonds and photochemically induced haptotropic shifts of pi-coordinated aromatic ligand systems

摘要

This thesis consists of six chapters. Chapter 1 reviews the development of organometallic chemistry and the bonding and symmetry features dealt with in later chapters.ududChapter two deals with the treatment of /ram'-NiF(C5F3RN)(PEt3)2, where R =F or H, with a variety of (CH^SiX compounds (X = N3, NCO or C=CSi(CH3)3), which resulted in the formation of complexes in which the activated fluorine atom was replaced; yielding ira«s-NiN3(CsF3RN)(PEt3)2, ira«5-NiNCO(C5F3HN)(PEt3)2 and irara-NiC=CSi(CH3)3(C5F3HN)(PEt3)2. The trifluoropyridylazide complex, trans- NiN3(C5F3HN)(PEt3)2, is reactive, forming the metal isocyanate complex, trans- NiNCO(C5F3HN)(PEt3)2 upon reaction with CO. Attempts were made to effect reductive elimination of the Ni(PEt3)2 fragment and form fluoropyridines substituted at the 2-position with the functionalities, N3, NCO and CsCSi(CH3)3.ududPrevious studies have shown that (ri5-C5F[5)(ri5-C4H4N)Fe has an extensive photochemistry that is dominated by haptotropic shifts of the coordinated pyrrolyl ligand. In an attempt to control the degree to which the hapticity of the pyrrolyl ligand can be altered, the photochemistry of (r|5-C5H5)(r|5-2 ,5 -(CH3)2C4H2N)Fe has been investigated. The results of matrix isolation studies of (r|5-C5H5)(r|5-2 ,5 - (CH3)2C4H2N)Fe are presented in chapter three. The photochemistry of this analogue is also dominated by haptotropic shifts. Both monochromatic and broad-band irradiation of this complex in CO doped Ar matrixes at 20 K gives rise to three species characterised as (r^-CsHsXV-AHCHs^lWFeCCO) (2 ), (t^-CsHjXti'-N- (CH3)2C4H2N)Fe(CO)2 (3 ) and (r|5-C5H5XTi3-A-(CH3)2C4H2N)Fe(CO) (4). Subsequent annealing of the matrix results in a conversion of the rl-monocarbonyl complex to the dicarbonyl complex and an isomerisation of the aza-allyl species to the corresponding 7r-allyl complex (r|5-C5H5Xr|3-C-(CH3)2C4H2N)Fe(CO) (5).ududChapter four presents the results of matrix isolation studies of (r|5-C4H4Se)Cr(CO)3 in inert (Ar and CH4) and reactive (CO and N2) matrixes at 20 K. The results indicate that the ri5-coordinated selenophene ring undergoes haptotropic shifts upon photolysis. The photoproducts observed depend on the host matrix employed. In all four matrixes, short wavelength irradiation (A,cxc = 405 nm) yields a three carbonyl band pattern that has been assigned to (r|4-C4H4Se)Cr(CO)3, whereby the selenophene ring has undergone a ring slip from r|5 —> r|Coordination, [(Ti4-C4H4Se)Cr(CO)3N2 in N2 matrixes]. Subsequent photolysis o f this photoproduct in inert matrixes produces the CO loss product, (r|4-C4pl4Se)Cr(CO)2. In N2 matrixes subsequent photolysis of the primary photoproduct results in the formation of the dicarbonyl species, [(r]5- C4H4Se)Cr(CO)2N2]. In CO matrixes the initial photoproduct yields Cr(CO)o upon extended photolysis. There is evidence to support a possible photochemical r)5 —> r]4 —>ud'y r| stepwise exchange of the selenophene ring.ududChapter five deals with the steady state photolytic studies of the complex, [(r|5-C5H5)Fe(r|6-(CH3)2CHC6H5)] PF6. These studies indicate that the arene ring undergoes replacement when donor ligands are present in solution and the metal complex undergoes decomposition in their absence. CO was employed as the ligand of choice. [(r|5-C5H5)Fe(CO)3]PF6 was formed upon photolysis in CO purged acetone and dichloromethane solutions while [(r)5 C5H5)Fe(CH3CN)2(CO)]PF6 was produced in CO purged acetonitrile solutions. The decomposition products include ferrocene, ‘free’ arene and Fe2+. These results along with laser flash photolysis studies point to a mechanism involving a solvated intermediate of the type [(r|5-C5H5)Fe(solv)3]+. In addition preliminary steady state photolysis studies were carried out on the heteroaromatic complex, [(ri5 C5H5)Ru(r|5-2,5-(CH3)2C4H2S)]BF4.ududOutlined in Chapter 6 are the experimental details and suggestions for future work.