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The oxidation mechanism of a series of mixed-ligand five-coordinate cobalt(I) complexes of the type [Co(CNR) 3 L 2 ] + (R = C 6 H 5 , 4-CH 3 C 6 H 4 , 4-CH 3 OC 6 H 4 , 4-NO 2 C 6 H 4 , and 2,6-(CH 3 ) 2 C 6 H 3 ; L = P(OCH 3 ) 3 and P(C 6 H 5 )(OC 2 H 5 ) 2 ) on mercury and platinum electrodes in dichloromethane is described. The primary reversible electron transfer between electrode and depolarizer is followed by a fast chemical reaction which brings about a change in configuration (and a dimerization). Correlations between redox properties of the species and their structural features are discussed.

Iron(II) monocarbonyl complexes of the type [FeX(CO)L4]BPh4[X = Cl or Br; L = P(OMe)3′ P(OEt)3′ or PPh(OEt)2] and the dicarbonyl compound [FeBr(CO)2{PPh(OEt)2}3] BPh4 have been prepared and characterized by i.r.,1H and 31P-{1H} n.m.r. spectroscopy. Reactivity with some π-acceptor ligands has been investigated and synthesis of the new derivatives [FeBr(4-Me-C6H4NC)3L2]+[L = P(OMe)3′ P(OEt)3′ or PPh(OEt)2] achieved.

Mossbauer parameters have been determined, at 80 K, for some new complexes of the type [FeX(CNR)5-nLn]ClO4(n  3, 2, 0; X  Br-, I-; L  PhP(OEt)2; R  4-CH3C6H4, 2-CH3C6H4, C6H5, 4-NO2C6H4, 4-CH3OC6H4, 2,6-(CH3)2C6H3 and [FeX2(4-CH3C6H4NC)4]. Treatment by the point-charge model has been carried out to rationalize quadrupole splitting and centre shift values for chloro, bromo and iodo derivatives. The structural assignments, by pqs parameters, are consistent with X-ray and IR data.

Arenediazonium complexes of cobalt(I) of the type [Co(RN2)L4][BPh4]2[L = P(OEt)2Ph, P(OEt)3, or P(OMe)3; R = 4-CH3C6H4, 3-CH3C6H4, 2-CH3C6H4, C6H5, 4-CH3OC6H4, 4-ClC6H4, or 4-FC6H4] have been prepared; their characterization by i.r., 1H, and 31P-{1H} n.m.r. spectra is reported. Reactivity with π-acceptor ligands such as CO, NO, isocyanide, and phosphite is also described. Finally, the reaction of the arenediazonium complexes with chloride ions affording the cobalt(II) derivatives [CoClL4]+ has been investigated; the function of RN2 as an oxidizing agent in this reaction is also discussed.

The synthesis and characterization of some new five-co-ordinate mononitrosyl cobalt complexes of the type [CoL4(NO)][BPh4]2[L = P(OMe)3, P(OEt)3, or PPh(OEt)2] is described. The reactivity of these compounds with π-acceptor ligands such as NO, CO, phosphite, and isocyanide is discussed. Furthermore, the reaction with molecular oxygen and with halide ions (X–) has been investigated and a new method of obtaining the cations [CoXL3(NO)]+ has been achieved. The cathodic and anodic behaviour of the complex [Co{P(OEt)3}4(NO)][BPh4]2 at a platinum electrode in acetonitrile is also reported.

The synthesis and characterization of complexes of the type [FeX(4-CH3-C6H4NC)nL5−n]ClO4 (X  Cl, Br, or I; n = 2, 3 or 4; L  PhPMe2, PhPEt2, Ph2PMe, Ph2PEt, or Ph2P(OEt) are described. The steric hindrance by the phosphine ligand is tentatively correlated with the influence of the π-acidity of phosphine and isocyanide ligands in determining the composition of these compounds. Their structures have been postulated on the basis of infrared and PMR spectra. Mossbauer parameters have also been determined at liquid nitrogen temperature by a treatment of the data by the point-charge model.

The title complexes [PtCl2(bama·HCl)] and [PtCl2(taa·2HCl)] with the tri- and quadri-dentate ligands acting as bidentate have been prepared and the kinetics of closure of the second condensed ring have been studied in aqueous solution. From stopped-flow measurements in basic media at 25 °C, the rate constants for the reactions [PtCl2-(bama)]→[PtCl(bama)]++ Cl– and [PtCl2(taa)]→[PtCl(taa)]++ Cl– are k1= 2.1 ± 0.1 and k1″= 4.3 ± 0.2 s–1. This implies that only a probability factor of two can satisfactorily account for the difference in the observed rates. Kinetic measurements at pH < 7 have show that under these conditions the reactive species are unprotonated [PtCl2(bama)] and monoprotonated [PtCl2(taa·HCl)]; the ring-closure process is faster for the tris(2-aminoethyl)amine (taa) complex than for the bis(2-aminoethyl)methylamine (bama) complex, and anchimeric assistance of the protonated end of taa on entry of the unprotonated end (by ion pairing with the leaving chloride) is proposed.

Mono- and tri-µ-chloro ruthenium(II) complexes [Ru2Cl3L8]BPh4 and [Ru2Cl3L6]BPh4[L = P(OEt)3 or P(OEt)2Ph] were prepared by allowing ruthenium trichloride to react with phosphite in refluxing ethanol. Cationic carbonyl derivatives of the type trans-[RuCl(CO)L4]+ were also prepared by the carbonylation reaction of a phosphite-containing RuCl3 solution. The reaction of all these compounds with isocyanide was examined and led to the synthesis of the new [RuCl(RNC)2L3]+, [Ru(RNC)3L3]2+, and [RuCl(CO)(RNC)L3]+ derivatives. Characterization of the complexes by i.r. and 1H and 31P n.m.r. data is also discussed.

Zinc dust reduction of both cis- and trans-complexes (I) gives the air-stable, diamagnetic hydride complexes (II).

Voltammetry at a stationary platinum electrode and polarography were carried out in dichloromethane (0.1 mol dm−3 tetrabutylammonium perchlorate as supporting electrolyte) for complexes of the type [FeX(CNR)2L3][ClO4] [X = Cl, Br or I; L = PPh(OEt)2; R = phenyl, 4-methylphenyl, 4-methoxyphenyl, 2-methylphenyl or 2,6-dimethylphenyl] and for [Fe(CNR)3L3][ClO4]2 [L = PPh(OEt)2; R = cyclohexyl]. A mechanism of the redox process for both oxidation and reduction is postulated. A simple redox change without any complication from chemical reaction occurs in the case of oxidation at a platinum elec t rode, whereas the reduction is complicated by a subsequent chemical reaction.

The molecular hydrogen complexes {MH(η2-H2)[PhP(OEt)2]4} BPh4(M = Fe, Ru, Os) and dihydride species {CoH2[PhP(OEt)2]4}BPh4 have been prepared and T1 measurements for H– and η2-H2 resonances give T1

Mono- and tri-µ-chloro ruthenium(II) complexes [Ru2Cl3L8]BPh4 and [Ru2Cl3L6]BPh4[L = P(OEt)3 or P(OEt)2Ph] were prepared by allowing ruthenium trichloride to react with phosphite in refluxing ethanol. Cationic carbonyl derivatives of the type trans-[RuCl(CO)L4]+ were also prepared by the carbonylation reaction of a phosphite-containing RuCl3 solution. The reaction of all these compounds with isocyanide was examined and led to the synthesis of the new [RuCl(RNC)2L3]+, [Ru(RNC)3L3]2+, and [RuCl(CO)(RNC)L3]+ derivatives. Characterization of the complexes by i.r. and 1H and 31P n.m.r. data is also discussed.

Binuclear complexes [(MHP4)2(μ-HNNAr−ArNNH)](BPh4)2 [M = Fe, Ru; P = P(OMe)3, P(OEt)3, PPh(OEt)2; Ar−Ar = 4,4‘-C6H4−C6H4, 4,4‘-(2-CH3)C6H3−C6H3(2-CH3), 4,4‘-C6H4−CH2−C6H4] were prepared by allowing hydride species MH2P4 to react with bis(diazonium) salts (N2Ar−ArN2)(BF4)2 in a 2:1 ratio at low temperature. The compounds were characterized by 1H and 31P{1H} NMR spectroscopy (including 15N isotopic substitution) and an X-ray crystal structure determination. The complex [{FeH(P(OEt)3)4}2{μ-4,4‘-HNN(2-CH3)C6H3−C6H3(2-CH3)NNH}](BPh4)2 crystallizes in the space group P1 with a = 16.105(5), b = 17.551(6), c = 11.539(3) A; α = 96.41(2), β = 84.49(2), γ = 97.97(2)°; and Z = 2. The structure is centrosymmetric and consists of binuclear cations with the two iron atoms in an octahedral environment having the hydride and the diazene ligands in mutually cis positions. The [(MHP4)2(μ-HNNAr−ArNNH)]2+ cations reacted with mono(diazonium) (RN2)BF4 salts to give the binuclear bis(diazene) derivatives [{M(RNNH)P4}2(μ-HNNAr−...

Hydride complexes [ReH(CO)4L] 1, [ReH(CO)3L2] 2, [ReH(CO)2L3] 3 and [ReH(CO)L4] 4 [L = P(OEt)3 a, PPh(OEt)2 b, PPh2(OEt) c or PPh2(OMe) d] were prepared by treating [ReH(CO)5] with the appropriate phosphite under UV irradiation or reflux. The complexes were characterised by IR, 1H, 13C and 31P NMR spectroscopy and by crystal structure determinations of 1d and 2d. Protonation of the monocarbonyls [ReH(CO)L4] 4 in CD2Cl2 with HBF4·Et2O resulted in an equilibrium mixture of the classical dihydride complexes [ReH2(CO)L4]+BF4– and their non-classical tautomers [Re(η2-H2)(CO)L4]+BF4–. The dihydride [ReH2(CO){PPh(OEt)2}4]BPh4 was also isolated as a solid by protonation of [ReH(CO){PPh(OEt)2}4] in ethanol. Thermally unstable [Re(η2-H2)(CO)4L]+, [Re(η2-H2)(CO)3L2]+ and [Re(η2-H2)(CO)2L3]+ 7 cations were also prepared by protonation of the corresponding monohydrides 1, 2 and 3 and fully characterised in solution. The unsaturated complexes [Re(CO)2L3]BPh4 and [Re(CO)L4]BPh4 11 and the triflate [Re(η1-OSO2CF3)(CO)3L2] were obtained from the η2-H2 derivatives by evolution of H2. The new complexes [Re(CCPh)(CO)3L2], [Re(CCPh)(CO)L4] 13, [Re(4-MeC6H4CN)(CO)2L3]BPh4, [Re(4-MeC6H4NC)(CO)2L3]BPh4 and [Re(4-MeC6H4NC)(CO)L4]BPh4 were prepared by treating the triflate compounds or the unsaturated compounds [Re(CO)2L3]BPh4 and [Re(CO)L4]BPh4 with Li+CCPh– or with the appropriate ligand.

The rhenium complexes [ReOCl3L2] and [ReCl3L3][L = PPh2OMe, PPh2OEt, PPh2OPri, PPh(OEt)2 or PPh(OPri)2] were prepared by allowing [ReOCl3(AsPh3)2] to react with the appropriate amount of phosphinite or phosphonite. Treatment of [ReCl3L3] with CO and p-MeC6H4NC afforded the mer-trans-[ReCl(CO)3L2] and [ReCl2(p-MeC6H4NC)4L]BPh4 complexes, respectively. Treatment of [ReOCl3L2] with NaBH4 gave [Re2H8L4], but in the presence of phosphinite or phosphonite the trihydrides [ReH3L4] were obtained. Treatment of [ReCl3L3] with NaBH4 gave instead pentahydride complexes [ReH5L3]. All the multihydrides were characterised as ‘classical’ species by variable-temperature NMR spectroscopy (1H and 31P) and T1 measurements. Protonation of [Re2H8L4] and [ReH3L4] with HBF4·Et2O gave the classical hydride cations [Re2H9L4]+ and [ReH4L4]+, respectively, while similar treatment of [ReH5L3] gave a species formulated as containing an η2-H2 ligand, [ReH4(η2-H2)L3]+ on the basis of T1(min) evidence.

Hydrazine complexes [RuH(R1NHNH2)L4]BPh4 1–3, [Ru(R1NHNH2)2L4][BPh4]2 4–6 [R1 = H, Me, Ph, 4-MeC6H4 or 4-O2NC6H4; L = P(OEt)3, PPh(OEt)2 or P(OMe)3] were prepared by allowing the hydride species [RuH2L4] to react, first with triflic acid (CF3SO3H) and then with an excess of the appropriate hydrazine. The derivatives [RuH(Me2NNH2){P(OEt)3}4]BPh4 1f, [Ru(η1-OSO2CF3)(Me2NNH2){P(OEt)3}4]BPh4 9 and [Ru(η2-Ph-CONHNH2)L4][BPh4]2 7,8 [L = P(OEt)3 or PPh(OEt)2] were also obtained. The formulation and geometry in solution of the compounds were established by infrared and 1H and 31P NMR spectroscopy. The reaction of the bis(nitrile) complexes [Ru(R2CN)2L4][BPh4]2 [R2 = Me or MeC6H4; L = P(OEt)3 or PPh(OEt)2] with hydrazines depends not only on the experimental conditions, but also on the nature of the phosphite and the hydrazine used. Thus, nitrilehydrazine [Ru(R1NHNH2)(R2CN)L4][BPh4]2 10–13 [L = P(OEt)3 or PPh(OEt)2] or amidrazone derivatives [Ru{η2-NHC(R2)N(R1)NH2}{P(OEt)3}4][BPh4]2 14,15 (R1 = H or Me) were obtained together with the bis(hydrazine) compounds [Ru(R1NHNH2)2L4][BPh4]2. Reaction of the arylhydrazine complexes 1–6 and 10–13 with Pb(O2CMe)4 at –30 °C in CH2Cl2 resulted in selective oxidation of the arylhydrazine ligand giving the aryldiazene derivatives [RuH(R1NNH)L4]BPh4, [Ru(R1NNH)2L4][BPh4]2 and [Ru(R1NNH)(R2CN)L4][BPh4]2 (R1 = Ph, 4-MeC6H4 or 4-O2NC6H4). Treatment of hydrazine NH2NH2 and methylhydrazine MeNHNH2 complexes 1–6 with Pb(O2CMe)4, instead, afforded the acetate [Ru(η2-O2CMe)L4]BPh4 derivatives which were characterised by a crystal structure determination of [Ru(η2-O2CMe){P(OEt)3}4]BPh4. The co-ordination of ruthenium is distorted octahedral with approximate C2v symmetry and the acetate is bidentate.

Hydrazine complexes [Fe(R1NHNH2)(R2CN)L4][BPh4]2 1–3 and [FeH(R1NHNH2)L4]BPh4 4 [R1 = H, Me, Ph, 4-MeC6H4, 4-ClC6H4, 4-O2NC6H4 or Me2NNH2; R2 = 4-MeC6H4, Me or Ph; L = P(OEt)3, P(OMe)3 or PPh(OEt)2] were prepared by reacting nitrile complexes [Fe(R2CN)2L4][BPh4]2 and [FeH(R2CN)L4]BPh4 with an excess of the appropriate hydrazine. Their formulation and geometry in solution were established by infrared and 1H and 31P NMR spectroscopy. Amidrazone derivatives [Fe{η2-NHC(R2)NR1NH2}L4][BPh4]2 [R2 = 4-MeC6H4, Me or Ph; R1 = H or Me; L = P(OEt)3 or P(OMe)3] were obtained by allowing nitrilehydrazine complexes to react in solution and their formation, involving a nucleophilic attack of the hydrazine on the cyanide carbon atom of the R2CN ligand, is also discussed. Reaction of the arylhydrazine complexes 1–4 with Pb(O2CMe)4 at –30 °C in CH2Cl2 resulted in selective oxidation of the arylhydrazine ligand affording the aryldiazene [Fe(R1NNH)(R2CN)L4][BPh4]2 and [FeH(R1NNH)L4]BPh4 10 [R1 = aryl; L = P(OEt)3 or P(OMe)3] derivatives. Treatment of the arylhydrazine [Fe(R1NHNH2)(R2CN){P(OEt)3}4][BPh4]2 1 (R1 = Ph or 4-MeC6H4) with an excess of NEt3 resulted in a complicated reaction giving the five-co-ordinate aryldiazenido derivatives [Fe(R1N2){P(OEt)3}4]BPh4.

Alkyl complexes IrCl2(η1-CH2Ar)(CO)(PPh3)2 (1) [Ar = Ph (a), p-tolyl (b)] were prepared by allowing the hydride mer- or fac-IrHCl2(PPh3)3 to react with terminal alkynes ArCCH in the presence of water. The complexes were characterized spectroscopically (IR and 1H, 31P, 13C NMR) and by the X-ray crystal structure determination of 1b. The acyl complex IrCl2{C(O)CH2C(CH3)3}(PPh3)2 (2) was also prepared by reacting mer-IrHCl2(PPh3)3 with tert-butylacetylene HCCC(CH3)3 in the presence of H2O. A reaction path for the hydration of terminal alkyne in the presence of the Ir(III) complex leading to the cleavage of the CC bond, with the formation of the complexes 1 or 2 is also proposed. Acetylide complexes IrHCl(CCAr)(PPh3)3 (3), IrHCl(CCAr)(AsPh3)3 (4) [Ar = Ph (a), p-tolyl (b)] and IrHCl(CCPh){PPh(OEt)2}(PPh3)2 (5) were prepared by reacting IrHCl2L3 (L = PPh3, AsPh3) or IrHCl2{PPh(OEt)2}(PPh3)2 with lithium acetylide. Protonation reaction with Bronsted acids of the acetylide 3 was also studied and led to unstable vinyl derivatives. The stable vinyl [IrCl{η2-CHC(H)COOMe}L2]BPh4 (6,7) [L = PPh3 (6), AsPh3 (7)] complexes, instead, were prepared by allowing IrHCl2L3 to react first with AgCF3SO3 and then with methyl propiolate.

The hydrazine complexes [Ru(NH2NH2)L5](BPh4)2 1, 8 or [Ru(NH2NH2)L′L4](BPh4)2 2 [L = P(OEt)3, L′ = PPh(OEt)2] were prepared by allowing the corresponding hydride species [RuHL5]BPh4 or [RuHL′L4]BPh4 to react first with HBF4 and then with hydrazine. Oxidation of these hydrazine complexes or [Os(NH2NH2)L5](BPh4)2 with Pb(OAc)4 at −30 °C led to the corresponding stable and isolable 1,2-diazene complexes [M(NHNH)L5](BPh4)2 3, 5 (M = Ru, Os) or [Ru(NHNH)L′L4](BPh4)2 4. The phenyldiazene derivatives [M(PhNNH)L5](BPh4)2 6, 7 (M = Ru, Os) were also prepared by treating the hydride [MHL5]BPh4 species with phenyldiazonium tetrafluoroborate. The aquo-complex, [Ru(H2O){P(OEt)3}5](BPh4)2 8, was obtained by substitution of the NHNH ligand in [Ru(NHNH)L5](BPh4)2 and was characterised by X-ray crystal structure determination. Oxidation reactions of the bis(hydrazine) complexes [Ru(NH2NH2)2L4](BPh4)2 or [Ru(CH3NHNH2)2L4](BPh4)2 [L = P(OEt)3] with Pb(OAc)4 were reinvestigated and were found to give the diazene complexes [Ru(NHNH)2L4](BPh4)2 9, [Ru(CH3NNH)2L4](BPh4)2 11 or [Ru(CH3NNH)(CH3NHNH2)L4](BPh4)2 10.

Arenediazonium complexes of cobalt(I) of the type [Co(RN2)L4][BPh4]2[L = P(OEt)2Ph, P(OEt)3, or P(OMe)3; R = 4-CH3C6H4, 3-CH3C6H4, 2-CH3C6H4, C6H5, 4-CH3OC6H4, 4-ClC6H4, or 4-FC6H4] have been prepared; their characterization by i.r., 1H, and 31P-{1H} n.m.r. spectra is reported. Reactivity with π-acceptor ligands such as CO, NO, isocyanide, and phosphite is also described. Finally, the reaction of the arenediazonium complexes with chloride ions affording the cobalt(II) derivatives [CoClL4]+ has been investigated; the function of RN2 as an oxidizing agent in this reaction is also discussed.

Hydride complexes [OsH2L4][L = P(OEt)3 or PPh(OEt)2] were prepared. Their reactions with arenediazonium cations led to the synthesis of [Os(RNNH)2L4][BPh4]2 and [OsH(RNNH)L4]BPh4(R = Ph, 4-MeC6H4, or 4-MeOC6H4) complexes which were characterized by 1H and 31P n.m.r. data (with 15N isotopic substitution). The compounds [Os(4-MeC6H4NNH)(4-MeC6H4NC)L4][BPh4]2 were also prepared. The reaction of the bis(aryldiazene) derivatives with NEt3 led to new five-co-ordinate aryldiazenido complexes [Os(RN2)L4]BPh4(R = Ph or 4-MeC6H4). Protonation of the diazenido compounds with CF3CO2H and HBF4 gave the six-co-ordinate mono(diazene)[Os(CF3CO2)(RNNH)L4]BPh4 and the five-co-ordinate [Os(RNNH)L4]BPh4(R = 4-MeC6H4) derivatives, respectively. Infrared and 1H and 31P n.m.r. data for these complexes are reported.

The title complexes [PtCl2(bama·HCl)] and [PtCl2(taa·2HCl)] with the tri- and quadri-dentate ligands acting as bidentate have been prepared and the kinetics of closure of the second condensed ring have been studied in aqueous solution. From stopped-flow measurements in basic media at 25 °C, the rate constants for the reactions [PtCl2-(bama)]→[PtCl(bama)]++ Cl– and [PtCl2(taa)]→[PtCl(taa)]++ Cl– are k1= 2.1 ± 0.1 and k1″= 4.3 ± 0.2 s–1. This implies that only a probability factor of two can satisfactorily account for the difference in the observed rates. Kinetic measurements at pH < 7 have show that under these conditions the reactive species are unprotonated [PtCl2(bama)] and monoprotonated [PtCl2(taa·HCl)]; the ring-closure process is faster for the tris(2-aminoethyl)amine (taa) complex than for the bis(2-aminoethyl)methylamine (bama) complex, and anchimeric assistance of the protonated end of taa on entry of the unprotonated end (by ion pairing with the leaving chloride) is proposed.

The electrochemical behaviour of the complex [Co{P(OEt)3}2(NO)2][BPh4] has been studied in acetonitrile, using platinum and mercury electrodes. It undergoes two subsequent reduction processes and a single oxidation process. In particular, the less cathodic one-electron reduction leads to the formation of the corresponding neutral species which is fairly stable in carefully deaerated solution.

The cathodic and anodic behaviour of some five-co-ordinated nitrosyl cobalt complexes of the type [CoXL3(NO)][BPh4][X = Cl or I, L = P(OEt)3 or P(OMe)3] has been investigated at platinum electrodes in acetonitrile solvent. Four-co-ordinated mononitrosyl cobalt compounds of formula [CoL3,(NO)] are formed via an e.c.e. type reduction mechanism (electron transfer followed by a chemical reaction followed by electron transfer). The anodic oxidation of these [CoL3(NO)] compounds has also been studied. The [CoXL3(NO)][BPh4] complexes with L = P(OEt)3 undergo a complicated oxidation process leading to the dinitrosyl [CoL2(NO)2][BPh4] and [CoXL(NO)2] compounds and to species containing no nitrosyl ligand. The chemical reactions associated with the charge-transfer steps involve traces of water.

The hydride trans-[FeH(CO)L4]BPh4[L = P(OEt)3] reacts with aryldiazonium cations to give aryldi-imine [fe(NHNAr)-(CO)L4]2+ derivatives, which undergo substitution reactions with ketones, CO, RCN, and isonitriles to produce hexaco-ordinate cations [Fe{OC(RR′)}(CO)L4]2+, [Fe(CO)2L4]2+, [Fe(CO)(RCN)L4]2+, and [Fe(CO)(RNC)L42+ respectively, while in the reaction with gaseous NO the pentaco-ordinate complex {FeL4NO]+ is obtained.