Functionalised σ-Aryl Complexes of Ruthenium and Osmium

Abstract

This thesis is concerned with the synthesis and reactivity of various functionalised σ-aryl complexes of the transition metals, ruthenium and osmium in the +2 oxidation state. Chapter One presents a brief review of transition metal alkyl and aryl chemistry. Topics covered include bonding, synthesis and reactivity of these compounds. A discussion of organometallic compound synthesis using mercury reagents, of particular relevance to this thesis, is also included. Selected examples of reported functionalised σ-aryl transition metal complexes are mentioned therein. Chapter Two begins with a brief review of nitroaryl complexes. This chapter then describes the nitration reactions of OsRY(CO)(PPh3)2 (R = C6H5, C6H4CH3-2; Y = C1, η2-O2NO, η2-O2CCH3) using a mixture of copper(II) nitrate in acetic anhydride. Mono- and dinitration were facile and OsRXY(CO)(PPh3)2 (R = C6H4NO2-4, C6H3CH3-2-NO2-4,X = Cl, Y = CO; R = C6H4NO2-4, C6H3CH3-2-NO2-4, X and Y = η2-O2NO, η2-O2CCH3) and OsRX(CO)(PPh3)2 (R = η2-C6H3NO2-2-NO2-4, η2-C6H2NO2-2-NO2-4-CH3-6; X = C1, ONO2, OC[O]CH3) were isolated from these reactions. Mononitration of several phenyl osmium complexes was also effected using nitronium hydrogen disulphate. A modified synthesis of Ru(C6H3N[O]O-2-NO2-4)C1(CO)(PPh3)2, which gives an improved yield of this compound, is described in Chapter Two. The results of extensive NMR studies on this compound are also presented. The ortho-nitrophenyl complexes, M(C6H4N[O]O-2)C1(CO)(PPh3)2 (M = Ru, Os), could not be synthesised using the above direct nitration procedures. However, these compounds were obtained by reaction of the mercury reagent Hg(C6H4NO2-2)2 with MHC1(CO)(PPh3)3. The complexes M(C6H4N[O]O-2)C1(CO)(PPh3)2 (M = Ru, Os) underwent facile bromination, in the presence of a catalyst, to give M(C6H3N[O]O-2-Br-4)X(CO)(PPh3)2 (M = Ru, X = Cl, Br; M = Os, X = Br). The aryl ligands of M(C6H4N[O]O-2)C1(CO)(PPh3)2 (M = Ru, Os) and compounds of the type RuRY(CO)(PPh3)2 (R = C6H4NHCOCH3-4, C6H4NH2-4; Y = η2-O2NO, η2-O2CCH3) were also nitrated directly using copper(II) nitrate and acetic anhydride to give M(C6H3N[O]O-2-NO2-4)C1(CO)(PPh3)2 and Ru{C6H3(NO2)-3-(NHCOCH3)-4}(η2-O2NO)(CO)(PPh3)2 respectively. In the second part of Chapter Two the nitration reactions of M(C6H4CH3-4)C1(CO)(PPh3)2 (M = Ru, Os) are described. By controlling the amount of the reagent, either mononitration or dinitration of the phenyl ring was achieved. The products of mononitration were M(C6H3N[O]O-2-CH3-4)C1(CO)(PPh3)2 and the products of dinitration reactions can be viewed as trapped Wheland intermediates of the type, M{C6H3N[O]O)-2-(OC[O]CH3)-3-(CH3)-4-(NO2)-4}C1(CO)(PPh3)2. Reaction of the trapped Wheland intermediates, M{C6H3(N[O]O)-2-(OC[O]CH3)-3-(CH3)-4-NO2)-4}C1(CO)(PPh3)2 (M = Ru, Os), with hydrochloric acid gave different functionalised complexes of the type M(C6H3N[O]O-2-Y-4)C1(CO)(PPh3)2 (Y = CH3, CH2C1, CHO), Os{C6H2(N[O]O)-2-[O]-3-[O]-4}C1(CO)(PPh3)2 and M{C6H3(N[O]O)-2-(OR)-3-(CH3)-4-(NO2)-4}C1(CO)(PPh3)2 (M = Ru, Os; R = Me, Et). Reaction of M{C6H3(N[O]O)-2-(OC[O]CH3)-3-(CH3)-4-(NO2)-4}C1(CO)(PPh3)2 with silver tetrafluoroborate removed the halide from the metal and, in the presence of acetonitrile, water or carbon monoxide, the corresponding cations [M{C6H3(N[O]O)-2-(OC[O]CH3)-3-(CH3)-4-(NO2)-4}Y(CO)(PPh3)2]+ (M = Ru, Y = NCCH3, H2O, CO; M = Os, Y = NCCH3) were formed. Chapter Three introduces σ-aminophenyl complexes by briefly reviewing literature in this area. The synthesis and characterisation of Ru(C6H4NHCOCH3-4)C1(CO)(dmf)(PPh3)2 from the reaction of RuHC1(CO)(PPh3)3 with Hg(C6H4NHCOCH3-4)2 is briefly mentioned. This chapter then discusses the reduction reactions of the 4-nitrophenyl osmium complexes synthesised in Chapter Two. These reductions were effected by treatment of the nitrophenyl complexes with zinc under acid conditions to give OsRC1(CO)2(PPh3)2 (R = C6H4NH2-4, C6H3CH3-2-NH2-4). The complex Os(C6H4NH2-4)C1(CO)2(PPh3)2 was treated with ethyl formate to give the formamide compound Os(C6H4NHCHO-4)C1(CO)2(PPh3)2 and with the osmium dichlorocarbene complex, Os(CCl2)Cl2(CO)(PPh3)2, the diosmium complex (PPh3)2(CO)2ClOs(C6H4NC-4)OsCl2(CO)(PPh3)2 was formed. The reduction reactions of Ru(C6H3N[O]O-2-NO2-4)C1(CO)(PPh3)2 were also investigated in this section of work. This compound has two different nitro substituents on the phenyl ligand, a metal-coordinated ortho-nitro substituent and a non-coordinated para-nitro substituent. The reducing systems used for these reactions were M and HX (M = Zn, Sn; X = C1, BF4). When the nucleophiles C1 or HOEt were present in the reduction mixtures, nucleophilic aromatic substitution occurred, as well as reduction, and mixtures of Ru{C6H2(N[O]O)-2-(X)-3-(NH2)-4}C1(CO)(PPh3)2 (X = C1 or OEt, respectively) and Ru(C6H3N[O]O-2-NH2-4)C1(CO)(PPh3)2 formed. The compounds Ru{C6H2(N[O]O)-2-(X)-3-(NH2)-4}C1(CO)(PPh3)2 (X = C1, OEt) reacted with acetic anhydride to give the corresponding acetamidophenyl complexes, Ru{C6H2(N[O]O)-2-(X)-3-(NHCOCH3)-4}C1(CO)(PPh3)2 (X = C1, OEt). The zinc and acid reducing system did not give selective reduction of the noncoordinated nitro substituent. When no nucleophiles were present, Ru(C6H3NH2-2-NO2-4)C1(CO)(PPh3)2 and Ru(C6H3NO-2-NH2-4)C1(CO)(PPh3)2 were isolated as the major products from these reactions. In contrast, the tin and acid reducing system did give selective reduction of the para-nitro substituent and in these reactions Ru(C6H3N[O]O-2-NH2-4)C1(CO)(PPh3)2 was isolated as the major product. The compounds M(C6H4N[O]O-2)C1(CO)(PPh3)2 (M = Ru, Os) also underwent reduction with zinc and either hydrochloric or tetrafluoroboric acid and gave M(C6H4NH2-2)C1(CO)(PPh3)2 as the final products. The reduction reactions of nitro substituents to amino substituents are generally postulated to proceed through nitrosophenyl intermediates and when the nitro functional group was ortho to the transition metal, the nitrosophenyl intermediates M(C6H4NO-2)C1(CO)(PPh3)2 (M = Ru, Os) and Ru(C6H3NO-2-NH2-4)C1(CO)(PPh3)2 were isolated as stable compounds. The complex Ru(C6H3NO-2-NH2-4)C1(CO)(PPh3)2, isolated from the reduction reactions of Ru(C6H3N[O]O-2-NO2-4)C1(CO)(PPh3)2, was treated with various acylation reagents, such as ethyl formate and acetic anhydride, to give Ru{C6H3(NO)-2-(NHCHO)-4}C1(CO)(PPh3)2 and Ru{C6H3(NO)-2-(NHCOCH3)-4}C1(CO)(PPh3)2 respectively. The latter part of Chapter Three discusses attempts to diazotise the amino group of Ru{C6H2(X)-2-(Y)-3-NH2-4)C1(CO)(PPh3)2 (X = NO, Y = H; X = NO2 Y = H or C1). The diazotisation reactions of the para-amino groups were successful and products subsequently formed and isolated from the intermediate phenyl diazonium-containing complexes include Ru(C6H3N[O]O-2-OH-3)C1(CO)(PPh3)2, Ru{C6H2N[O]O)-2-[O]-3-[O]-4}C1(CO)(PPh3)2 and Ru(C6H3NO-2-NO2-3)C1(CO)(PPh3)2. Chapter Four discusses syntheses of the σ-bound 4-halophenyl complexes of ruthenium and osmium, M(C6H4X-4)C1(CO)(dmf)(PPh3)2 (M = Ru or Os; X = Br or I), using transmetallation reagents of the type Hg(C6H4X-4)2 (X = Br or I). These dmf adducts underwent ligand exchange reactions to form the derivatives, M(C6H4X-4)YZ(CO)(PPh3)2 (M = Ru, Os; X = Br, I; Y = C1, Z = CO or Y and Z = η2-OCCH3). Reaction of Os(C6H4Br-4)C1(CO)2(PPh3)2 with n-butyl lithium resulted in alkylation at the transition metal to give Os(C6H4Br-4)(Bu)(CO)2(PPh3)2. The compound Os(C6H4I-4)C1(CO)2(PPh3)2 reacted with n-butyl lithium to give the lithiated intermediate Os(C6H4Li)C1(CO)2(PPh3)2 which could not be isolated. Reaction of Os(C6H4Li)C1(CO)2(PPh3)2 with various electrophiles gave the new complexes Os(C6H4Y-4)C1(CO)2(PPh3)2 (Y = HgCl, CHO, C(CD3)2OH, C[O]CH3, CO2H). The reactivity of these products was studied. The complex Os(C6H4CHO-4)C1(CO)2(PPh3)2 underwent oxidation, reduction and condensation reactions to give Os(C6H4CO2H-4)C1(CO)2(PPh3)2, Os(C6H4CH2OH-4)C1(CO)2(PPh3)2 and Os(C6H4CHNOH-4)C1(CO)2(PPh3)2, respectively. In the presence of base, Os(C6H4CO2H-4)C1(CO)2(PPh3)2 reacted with coordinatively unsaturated compounds of the type MPhC1(CO)(PPh3)2 (M = Ru, Os) and the dimetallic compounds M{η2-O2CC6H4[OsC1(CO)2(PPh3)2]-4}Ph(CO)(PPh3)2 were isolated from these reactions. A discussion of the nitrodehalogenation reactions of M(C6H4X-4)C1(CO)Y(PPh3)2 (M = Ru, X = I, Br, no Y; M = Os, X = I, Br, Y = dmf), by reaction with copper(II) nitrate in acetic anhydride, is included at the end of this chapter.