Noel W. Duffy

IN SITU INFRARED SPECTROSCOPIC ANALYSIS OF THE ADSORPTION OF RUTHENIUM(II)BIPYRIDYL DICARBOXYLIC ACID PHOTOSENSITISERS TO TIO2 IN AQUEOUS SOLUTIONS

Abstract Internal reflection spectroscopy has been used to obtain the in situ infrared spectra of ruthenium(II) bipyridyl dicarboxylic acid photosensitiser species adsorbed to Degussa P25 and sol-gel TiO 2 films from dilute aqueous solutions. The spectra indicate that adsorption is via the carboxylate groups which bridge surface titanium ions. Adsorption isotherms and binding constants have been derived from the spectral data. The ruthenium(II) cis-di(thiocyanato)-N,N′-bis(2,2′-bipyridyl-4,4′-dicarboxylic acid) complex, which is an efficient sensitiser, has the highest binding constant. This suggests a link between the strength of surface binding and the solar energy conversion efficiency.

ELECTRONIC INTERACTIONS IN DIYNE CO2(CO)6 COMPLEXES

Abstract Electrochemical criteria are used to evaluate the electronic interaction between redox centres in the π-conjugated diyne complexes {RCC[Co 2 (CO) 6 ]CC[Co 2 (CO) 6 ]R} and {RCC[Co 2 (CO) 6 ](S)C[Co 2 (CO) 6 ]} (RPh, Fc) where the aromatic spacer S is phenyl, napthalene or anthracene. Voltammetry at microelectrode, differential pulse techniques and low temperature measurements are used to obviate the chemical complications following the primary redox process. A mechanism is proposed which successfully simulates the electrochemical data.

Synthesis, structure and electrochemistry of ferrocenylethynylsilanes and their complexes with dicobalt octacarbonyl

Abstract Coupling of lithium ethynylferrocene to alkyl and aryl chlorosilanes and to silicon tetrachloride leads to the formation of a variety of ferrocenylethynylsilanes, [(η5-C5H5)Fe(η5-C5H4C2)]4−nSiRn (n=0–3, R=Me, Ph). An additional series of compounds [(η5-C5H5)Fe(η5-C5H4C2)]4−nSi(n-Bu)xRy (n=0–3, x+y=n, R=Me, Ph) result from competitive reactions of excess n-BuLi at the silicon centre. Dicobalt octacarbonyl reacts with the ferrocenylethynylsilanes to give dicobalt hexacarbonyl derivatives, but for the tris- and tetrakis-compounds coordination of Co2(CO)6 is limited to two of the alkyne units as a result of steric crowding around the silicon centre. The crystal and molecular structure of the complex [(η5-C5H5)Fe(η5-C5H4C–(Co2(CO)6)C]2Si[(CC-η5-C5H4)Fe(η5-C5H5)]2 has been determined from X-ray data. Electrochemical investigation of the ferrocenylethynylsilanes and their dicobalt complexes shows that the equivalent ferrocenyl redox centres in these molecules are non-interacting.

The synthesis and electrophilic reactivity of manganese tricarbonyl complexes of the C-ring aromatic diterpenoid methyl O-methylpodocarpate

Abstract The aromatic ring in the diterpenoid methyl O -methylpodocarpate (podo) coordinates readily to the Mn(CO) 3 + moiety to afford in high yield a nearly 1:1 isometric distribution of [( η 6 -podo)Mn(CO) 3 ] BF 4 ([ 2 ]BF 4 ), in which the metal is situated on the α or β face. The nucleophiles PhLi, PhMgBr, MeLi, MeMgCl, LiCH 2 C(O)CMe 3 and NaBH 4 were found to add cleanly to the activated aromatic ring in 2 + to give neutral cyclohexadienyl complexes. Nucleophilic addition occurs predominantly meta to the OMe substituent in the case of the α-isomer of 2 + , and at both ortho and meta sites in the case of the β-isomer. The X-ray structure is reported for a typical α- meta and a typical β- ortho cyclohexadienyl product, namely β -( η 5 -podo · Ph)Mn(CO) 3 and α -( η 5 -podo · CH 2 C(O)CMe 3 )Mn(CO) 3 . The high yield and regioselectivity of the nucleophilic additions suggests that the manganese-mediated functionalization of aromatic diterpenes and steroids will prove to provide a useful synthetic methodology.

Synthesis and redox chemistry of 1,1′-bis(diphenylphosphino)ferrocene derivatives of R2C2Co2(CO)6 (R MeO2C, CF3)

Abstract Fe(C5H4PPh2)2 (dppf) undergoes facile thermal substitution reactions with R2C2Co2(CO)6 (R  MeO2C, CF3) to yield a variety of products. When R  MeO2C, initial coordination gives μ2-(MeO2C2)2C2Co2(CO)5(η1-dppf); its crystal and molecular structure, monoclinic, P2 1 /c, a = 8.954(3), b = 20.211(2) c = 23.836(5) A , β = 100.55(2)°, Z = 4, R1 = 0.0345 for 5764 reflections 1 > 2σ(1), confirms the monodentate coordination mode for dppf. At low dppf/alkyne-complex ratios, oligomeric products with dppf ligands linking up to five (μ2-MeO2C)2C2Co2 modules have been characterised but, as the proportion of the phosphine ligand increases. unstable products, which include a η1-μ-η1 dppf configuration, are obtained as well. In contrast, for R  CF3, only [(CF3)2C2]Co2(CO)4(η2-dppf) is found in significant yield. A molecule with two different reduction centres, [μ2-(MeO2C)2C2Co2(CO)5](μ-dppf)[Co3(μ3-CPh)(CO)8], was also characterised. Electrochemistry of the dppf complexes was characterised by fast ligand dissociation upon reduction of the (μ-alkyne)Co2 redox centre and oxidation of coordinated dppf. There was no evidence for communication between redox centres.

Relationships between basicity, redox behaviour of ferrocenylamines and their reactivity with Pt[II] compounds

Abstract p K b values for the ferrocenylamines, [( η -C 5 H 4 (CH 2 ) x NH 2 )FeCp] x = 1 , 2 , 3 ; [( η -C 5 H 4 CH 2 NHR)FeCp] R=Me, 4 , Ph, 5 ; {[ η -C 5 H 4 CHR′NR 2 ]FeCp} R′/R=H/Me, 6 , R′/R=H/Ph, 7 , Me/Me, 8 ;[{ η -C 5 H 4 CHRNMe 2 ) 2 Fe] R=H 9 , Me 10 ; [{1,2 η -C 5 H 3 (CH 2 NMe 2 )(PPh 2 )}FeCp] 11 , {1,2 η -C 5 H 3 [CH(Me)NMe 2 ](PR 2 }}Fe[ η -C 5 H 4 (PPh 2 ) n ] n =0, R= i Pr 12 , Ph 13 , n =1, R=Me 14 , are correlated with inductive, neighbouring group and steric effects. Corresponding salts have been synthesised. The p K b has a marked influence on their chemistry. Protonation competes with complexation but cis -PtCl 2 L 2 L= 1 – 3 , 5 , 7 , and cis -Pt(N–N)Cl 2 L= 8 , 9 , have been characterised. Two reversible couples [Fc + A/FcA], [Fc + AH + /FcAH + ] (A=amine function) and an irreversible oxidation/protonation of A are linked by a EECE mechanism, but potentials for the first two are independent of the amine and similar to ferrocene. Nucleophilic attack by ferrocenylamines at the nitrile, protonation and ligand substitution are all observed with cis- [PtCl 2 (NCR) 2 ].

Preparation and redox properties of phosphite derivatives of R2C2Co2(CO)6−n[P(OMe)3]n (R=CF3, MeO2C)

Abstract A series of phosphite complexes R 2 C 2 Co 2 (CO) 6− n [P(OMe) 3 ] n (R=CF 3 , MeO 2 C), n =1–4, have been prepared and characterised. Cyclic and square-wave voltammetry shows that the kinetic stability of the radical cations increases with substitution and when R=CF 3 . The radical cation {(CF 3 ) 2 C 2 Co 2 (CO) 2 [P(OMe) 3 ] 4 }PF 6 4a + has been characterised and its crystal structure compared with that of the neutral parent. Analysis of the anisotropic ESR spectrum of 4a + is consistent with an unpaired electron in a SOMO with little d z 2 character.

Synthesis, structure and redox chemistry of ferrocenylsilylmethylidinetricobaltnonacarbonyl complexes, FcSi(R)2CCo3(CO)9, 1,1′-Fc′[Si(R)2CCo3(CO)9]2 (R = Me, Et, Ph) and their derivatives

Abstract Reaction between the ferrocenyl silanes FcSiR 2 H and 1,1′-Fc′[SiR 2 H] 2 (R = Me, Et, Ph) and HCCo 3 (CO) 9 gives the corresponding ferrocenylsilylmethylidinetricobaltnonacarbonyl complexes FcSi(R) 2 CCo 3 (CO) 9 and 1,1′-Fc′[Si(R) 2 CCO 3 (CO) 9 ] 2 in good yield. Spectroscopic data include 29 Si NMR. The crystal structure of 1,1′-Fc′[Si(Me) 2 CCo 3 (CO) 9 ] 2 has been determined by an X-ray diffraction study. Thermal and electron-transfer catalysed substitution reactions with Lewis bases were successful except for the cluster 1,1′-Fc′[Si(Ph) 2 CCo 3 (CO) 9 ] 2 , where an unusual cleavage of the FcSi bond takes place. Electrochemical and ESR studies of the complexes FcSi(R) 2 CCo 3 (CO) 9 and 1,1′-Fc′[Si(R) 2 CCo 3 (CO) 9 ] 2 (R = Me, Ph) showed a one-electron oxidation centred on the ferrocenyl moiety and a one- or two-electron reduction dependent on the number of CCo 3 redox centres. The observed electrochemistry is consistent with electrochemically non-interacting redox centres. Chemical oxidation of FcSi(Me) 2 CCo 3 (CO) 9 , 1,1′-Fc′[Si(Me) 2 CCo 3 (CO) 9 ] 2 and FcSi(Me) 2 CCo 3 (CO) 8 L (L = P(OMe) 3 , PPh 3 , PCy 3 ) gave the respective monocations, whereas oxidation of FcSi(Me) 2 CCo 3 (CO) 7 [P(OMe) 3 ] 2 produced a dication.

Monitoring ECE transformations of metal carbonyls by in situ spectroelectrochemistry; SNIFTIRS of [Co3(CO)9C]2

Abstract An in situ subtractively normalised interfacial FTIR spectroscopy (SNIFTIRS) investigation of [Co 3 (CO) 9 C] 2 in dichloromethane is used to illustrate the application of these techniques to follow ECE transformations of metal carbonyls in a thin layer cell. SNIFTIRS data obtained at a platinum electrode show that the major species at ambient temperature is not the radical anion [Co 3 (CO) 9 C] 2 − . Within the timescale of the measurement [Co 3 (CO) 9 C] 2 − transforms to a new species with a bridged carbonyl configuration; this species forms a chemically reversible redox couple in the thin layer. The consequences for the redox chemistry of [Co 3 (CO) 9 C] 2 are discussed.

Reactions of HCCo3(CO)9 with silanes; synthesis and electrochemistry of X[SiMe2CCo3(CO)9]2 (X=O, 1,4-C6H4)

Abstract Reactions between Ph n SiH 4− n or HR 2 SiXSiR 2 H and HCCo 3 (CO) 9 are described. Both the monocluster, HMe 2 SiXSiMe 2 CCo 3 (CO) 9 , and the dicluster, (CO) 9 Co 3 CMe 2 SiXSiMe 2 CCo 3 (CO) 9 , complexes were obtained from the silanes HMe 2 SiXSiMe 2 H (X=O, 1,4-C 6 H 4 ). RSiH 2 CCo 3 (CO) 9 (R=Ph, Me) or sterically demanding silanes do not couple with HCCo 3 (CO) 9 . Generally with Ph n SiH 4− n ( n =1, 2) electrophilic attack on the cluster core resulted in the formation of the novel μ-silylene complexes HCCo 3 (CO) 8 (μ-SiR 2 ), and fragmentation of the Co 3 C unit, instead of the expected silicon-bridged diclusters. Electrochemical investigation of the dicluster compounds and their phosphite derivatives showed there was no interaction between the cluster redox centres.