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Complexes [Cp*Ir(ppy)NO3] (ppy = 2-phenylpyridine, 1), [Cp*Ir(2′,4′-F2-ppy)NO3] (2b), [Cp*Ir(κ2-C2,C2′-NHC)Cl], (κ2-C2,C2′-NHC = κ2-C2,C2′-1,3-bis(4-(N,N-dimethylamino)phenyl)-imidazol-2-ylidene, 3), [Cp*Ir(bpyr)(SOMe2)] (bpyr = bis-diethyl-pyrrole, 4), [Cp*Ir(bimH2)Cl]Cl (bimH2 = 2,2′-bisimidazole, 5) and [Cp*IrCl(μ2-κ2-κ1-bimH)IrCl2Cp*] (6) have been synthesized and characterized in solution by multinuclear and multidimensional NMR spectroscopy. The structures in the solid state of 3 and 6 have been determined by means of single-crystal diffraction X-Ray studies. Complexes 1–6 were found to be effective catalysts for water oxidation to molecular oxygen driven by cerium ammonium nitrate. The highest activity was observed for 4 (TOFmax = 12 min−1, TON > 500), 5 (TOFmax = 23 min−1, TON > 500) and 6 (TOFmax = 51 min−1, TON > 500) bearing more electron-donating ligands.

The reaction of a series of dimethyl zirconocenes [Me2Si(Cp)2ZrMe2, 1; Cpt−bu2ZrMe2, 2; Cpn−bu2ZrMe2, 3; Ind2ZrMe2, 4; CpMe42ZrMe2, 5; Cp∗2ZrMe2, 6] with [HNMe2Ph][B(C6F5)4] was investigated by means of NMR spectroscopy. It was found that protonolysis of a Zr–Me group occurred generating a coordinative vacancy at the metal center and methane. Cations coming from 1–4 dimethyl precursors bound NMe2Ph, liberated from the protonation process, and formed zirconaaziridinium ion pairs {[Me2Si(Cp)2Zr(η2–CH2NMePh)][B(C6F5)4], 7; [Cpt−bu2Zr(η2–CH2NMePh)][B(C6F5)4], 8; [Cpn−bu2Zr(η2–CH2NMePh)][B(C6F5)4], 9; [Ind2Zr(η2–CH2NMePh)][B(C6F5)4], 10}, reasonably as a consequence of CH activation of one Me group of coordinated NMe2Ph and methane elimination. The intramolecular/interionic structures and dynamics of 7–10 ion pairs were investigated by 1H, 13C and 19F 1D-and 2D-NMR techniques. The reactions of 7 and 10 ion pairs with 2-methyl-1-heptene afforded stable diastereoisomeric ion pairs bearing a five-member azametallacycle.

Four diarylethenes, which were expected to be thermally irreversible photochromic compounds, containing thiophene groups as aryls and dithiole-2-thione or dithiole-2-one at the ethenic bond, were investigated by steady state and time-resolved spectroscopy to obtain information about their photochemistry and the competitive relaxation paths of their electronically excited states. Only for the 4,5-bis(2-methyl-1-benzothien-3-yl)-1,3-dithiole-2-thione (BTDT), a good photochromic response was observed. The photocolouration reaction was undetectable for the 4,5-bis(2,5-dimethylthien-3-yl)-1,3-dithiole-2-thione (TDT), whereas for the two analogous compounds with oxygen (-ones) the occurrence of side reactions reduced their photochromic properties. For the photoreactive compounds, the quantum yields of the UV-photoinduced ring-closing reaction and the visible-stimulated cycloreversion reaction were determined. Nanosecond time-resolved experiments showed the formation of transients which were assigned to n , π * triplets for thiones and π , π * triplets for ones, respectively. 1 H NMR measurements allowed the equilibrium ratio between parallel and antiparallel conformations for the benzo-annellated compounds to be determined.

Fe(CO) 4 X 2 complexes [X = I ( 1 ), Br( 1 ′)] react with phosphine ligands L (L = PMe 3 , PEt 3 , PMe 2 Ph, PMePh 2 , PPh 3 ) via a two-step mechanism: in the first step fac -Fe(CO) 3 LX 2 complexes are formed; in the second step two parallel pathways, a and b , are observed; in pathway a , reductive elimination with formation of equimolar amounts of Fe(CO) 3 L 2 ( 5 ) and phosphonium salts [LX] + X − is observed; in pathway b , disubstituted dihalide complexes cis , trans , cis -Fe(CO) 2 L 2 X 2 are formed. The relative weights of pathways a and b depend on the basicity, steric hindrance and concentration of ligand L, on the nature of the halogen and on temperature. A radical mechanism which accounts for most of the experimental results is proposed.

Three stereoisomers (EEE, EZE and ZEE) of 1-(1′-naphthyl),6-phenyl-hexatriene have been prepared by standard procedures and characterized by spectrophotometry and NMR spectroscopy. The properties of their lowest excited states of singlet and triplet multiplicity have been investigated by fluorimetry, laser flash photolysis and conventional photochemical techniques, and compared with those of the symmetric 1,6-diphenyl-hexatriene and the shorter chain analogues.

The reactions of cis , trans -[M(CO) 2 (PMe 3 ) 2 CH 3 I] [M=Fe ( 1 ), Ru ( 2 )] and cis , trans , cis -[Fe(CO) 2 (PMe 3 ) 2 (CH 3 ) 2 ] ( 3 ) with B(C 6 F 5 ) 3 involve Me-abstraction from the metal with formation of reactive species that undergo decomposition processes. In the presence of H 2 O complex 2 reacts with B(C 6 F 5 ) 3 forming cis , trans -[Ru(CO) 2 (PMe 3 ) 2 I(HOB(C 6 F 5 ) 3 )] ( 7 ) that slowly transforms in cis , trans -[Ru(CO) 2 (PMe 3 ) 2 I(H 2 O)] + [(HOB(C 6 F 5 ) 3 )] − ( 8 ), while complex 1 affords the cyclometallate complex trans -[Fe(CO)(PMe 3 ) 2 I(C(Me)OB(C 6 F 5 ) 2 OH)] ( 9 ) whose molecular structure was investigated by X-ray diffraction studies.

The reaction of [Pd(η1,η2-C8H12OMe)Cl]2 with α-iminoketone ligands affords cationic η1,η2-5-methoxycyclooctenyl Pd(II) complexes, the intramolecular and interionic structures of which were investigated in both solution and solid state; such complexes undergo unprecedented isomerisation to η1,η2-1-methoxycyclooctenyl complexes assisted by weak nucleophiles such as olefins or alkynes.

Complexes [M(η1,η2-C8H12OMe)((2,6-(R)2C6H3)NC(R′)C(R′)N((2,6-(R)2C6H3))]PF6 (where M=Pd, R=H and R′2=Me2 (1), M=Pd, R=Me and R′2=Me2 (2), M=Pd, R=Et and R′2=Me2 (3), M=Pd, R=iPr and R′2=Me2 (4), M=Pd, R=iPr and R′2=An (5), M=Pt, R=iPr and R′2=An (6)) were synthesized by the reaction of [M(η1,η2-C8H12OMe)Cl]2 with the appropriate α-diimine ligand in the presence of NH4PF6. Their ion pair structure in solution was investigated by detecting dipolar interactions between protons belonging to the cation and fluorine nuclei of the anion (interionic contacts) in the 19F, 1H-HOESY NMR spectra. In complexes 1–4, the anion in solution is located close to the peripheral protons of the α-diimine ligand and it interacts with the R′ protons and with the R protons that point toward the R′ groups. The steric protection of apical position exerted by the R substituents is clearly illustrated by the absence of interionic contacts between any protons of the cycloctenylmethoxy-moiety and the anion for R≥Me in 1–4. In complexes 5 and 6 the interactions between the anion and the peripheral N,N protons also predominate but other anion–cation orientations are significantly present and, consequently, the interionic structure is less specific.

The molecular crystal structure of (Bzim)Ph2P=L=1-benzyl-2-imidazolyldiphenylphosphine (monoclinic; space group P21/c #14; a=9.054(2), b=9.394(3), c=21.677(8) A; β=94.52(2)°; Z=4) is reported here. This new P,N ligand reacts with CuI or AgI metal ions to give [M2L3]2+ dinuclear complexes where the bihapto ligand always bridges the metal centers. When L was added to [Au2L2]2+ complex the dinuclear gold cycle underwent a cleavage and the mononuclear species [AuL2]+ was obtained. The solution behavior of the complexes was investigated by 1H and 31P NMR at variable temperature, showing neither dissociative nor equilibrium reactions. The strong coordinating ability of the (Bzim)Ph2P ligand was also indicated by cyclic voltammetry investigation and the electrogenerated Ag(0) neutral complex, namely [Ag2(μ-(Bzim)Ph2P)3], was detected as transient compound. The molecular crystal structure of [Cu2(μ-(Bzim)Ph2P)3][BF4]2 is also reported (monoclinic; space group P21/n #14; a=19.413(9), b=19.81(1), c=21.678(7) A; β=115.51(2)°; Z=4).

cis,trans- Os(CO) 2 (PMe 3 ) 2 CH 3 I ( 1 ) and fac -[Os(CO) 3 (PMe 3 ) 2 CH 3 ] + BPh 4 − ( 3 ) react with borohydrides (NaBH 4 , NBu 4 BH 4 , LiBEt 3 H) in diethyl ether to form the methyl hydride complex Os(CO) 2 (PMe 3 ) 2 (CH 3 )H ( 7 ). Similarly the monosubstituted fac- Os(CO) 3 (PMe 3 )CH 3 I ( 9 ) reacts with borohydrides to give fac -Os(CO) 3 (PMe 3 )(CH 3 )H ( 10 ). The isoelectronic complexes of iron cis,trans- Fe(CO) 2 (PMe 3 ) 2 CH 3 I ( 2 ) and fac- [Fe(CO) 3 (PMe 3 ) 2 CH 3 ]BPh 4 ( 4 ) give instead the dihydride complex cis,trans- Fe(CO) 2 (PMe 3 ) 2 H 2 ( 8 ). Complexes ( 1 )–( 4 ) react with lithium methyl to form the dimethyl complexes cis,trans- M(CO) 2 (PMe 3 ) 2 (CH 3 ) 2 [M=Os ( 5 ), Fe ( 6 )]. The structures of the complexes are studied by IR and 1 H-, 13 C{ 1 H}-, 31 P{ 1 H}-NMR spectroscopies. The different results are explained on the basis of a fast reductive elimination reaction in the case of iron and a fast decarbonylation reaction in the case of osmium.

Cyclic silver(I) compounds having a [μ-(Bzim)Ph 2 PAg] 2 2+ unit ((Bzim)Ph 2 P=1-benzyl-2-imidazolyldiphenylphosphine) and NO 3 − ( I ), BF 4 − ( II ), and B[3,5-(CF 3 ) 2 C 6 H 3 ] 4 − ( III ) as counterions were characterized in the solid state by X-ray crystal structure determinations ( I , II ), and in solution by 1 H-, 13 C-, 19 F- and 31 P-NMR spectroscopies. The crystal structure of complex [μ-(Bzim)Ph 2 PAg(NO 3 )] n ( n =2, 4) ( I ) (triclinic, space group P 1 (no. 2), a =15.118(5), b =17.755(3), c =14.123(4) A, α =90.23(2), β =111.67(2), γ =85.92(2)°, Z =2) shows two conformers A and B in the unit cell. The conformer A consists of a tetranuclear species formed by two [μ-(Bzim)Ph 2 PAg] 2 2+ moieties, related by a center of symmetry, bonded together by two bridging nitrate anions. The nitrate anions are coordinated to the silver atoms in an unusual fashion. The conformer B is a dinuclear species where the silver atoms present in the eight-membered ring complete their tetracoordination with two chelate nitrate anions. The crystal structure of complex {[μ-(Bzim)Ph 2 PAg(BF 4 )] 2 } ∞ ( II ) (monoclinic, space group P 2 1 / c (no. 14), a =11.563(3), b =8.353(4), c =26.188(7) A, β =95.88(2)°, Z =2) consists of infinite chains of the dinuclear cyclic silver moieties held together by BF 4 − bridging anions. The low temperature experimental and simulated 31 P-NMR spectra of complexes I – III show complex apparent doublets of multiplets due to the resonance of the spin systems of the three isotopomers of the silver atoms present in the cyclic units. The interionic solution structure of complex II was investigated by 19 F{ 1 H}-HOESY NMR spectroscopy. In methylene chloride solution the BF 4 − anion is not more coordinated to the silver(I) atoms as in the solid state, and it is localized in between the phenyl and benzyl groups of the ligand.

The equilibrium and kinetics of isocyanide insertion of complexes [Fe(PMe 3 ) 2 (CO) 2 (CH 3 )(CNR)] + X − ( 1 ) [CNR= tert -butylisocyanide; X − =I − ( 1a ), BPh 4 − ( 1b ); BF 4 − ( 1c )] which afford complexes [Fe(PMe 3 ) 2 (CO) 2 (η 2 -C(CH 3 )NC(CH 3 ) 3 )] + X − ( 2 ) were investigated in dichloromethane, methanol, acetone and nitromethane. The results indicate that the reaction proceeds via an associative mechanism with the preliminary formation of contact ion pairs. The structure of the contact ion pair in solution was studied by 1 H-NOESY and 19 F{ 1 H}-HOESY NMR spectroscopy. The results indicate that structure is independent of the nature of the solvent and of the counterion. In complexes 1b,c the counterion is located between the CO and the isocyanide ligands; in complexes 2b,c the counterion is located near the dihaptoiminoacyl ligand. The reaction rate increases with the charge density and the coordinating power of the anions. The effect of the solvent can be also explained on the basis of its coordinating power.