Neil G. Connelly

The Electron-Transfer Reactions of Polynuclear Organotransition Metal Complexes

Publisher Summary This chapter discusses the electron-transfer reactions of polynuclear organotransition metal complexes. The chemistry of polynuclear organometallic complexes has become increasingly important, particularly in aiding the understanding of the relationship among structure, bonding, and reactivity. A great deal of effort has been devoted to the study of linked metallocene units to probe the redox properties of compounds containing two or more identical electron-transfer sites. The imido-bridged complexes are reduced in a reversible one-electron process. The monoanion (E = P), prepared by sodium naphthalenide reduction of the neutral compound and isolable as a sodium salt, has an electron spin resonance (ESR) spectrum consisting of 15 triplets. There is very little information available on the redox properties of organometallic clusters of the early transition metals. The trinuclear carbonyls and the mixed metal clusters undergo one-electron reduction. Theoretical studies have shown that the monocations of both biferrocene and bis(fulvalene)diiron show some delocalization; the latter is much more delocalized than the former.

Structural evidence for the participation of P–X σ* orbitals in metal–PX3 bonding

Examination of metal–phosphorus and phosphorus–substituent atom bond length in a series of reduction–oxidation related pairs of transition metal phosphine complexes yields evidence of the participation of P–substitution σ* orbitals in the π-acceptor function of the phosphine.

Synthesis and electrophilic reactivity of dicarbonylnitrosyl(cyclohexadienyl)manganese cations: double nucleophilic addition to coordinated arenes

Synthese des cations (cyclohexadienyl)Mn(CO)(NO)L + par traitement de (cyclohexadienyl)Mn(CO) 2 L (L=CO, PBu 3 ) avec NOPF 6 . Mecanisme des reactions de ces cations avec les nucleophiles

Reduction–oxidation properties of organotransition-metal complexes. Part 29. Pentaphenylcyclopentadienyl complexes of ruthenium

The complex [Ru3(CO)12] reacts with C5Ph5Br in toluene under reflux to give [RuBr(CO)2(η-C5Ph5)](1) which undergoes carbonyl substitution with P-donor ligands, in acetone in the presence of ONMe3·2H2O, to yield [RuBr(CO)L(η-C5Ph5)][2; L = PPh3, PEt3, or P(OMe)3]. The halide abstraction reactions of (2) with AgPF6 and L1 afford [Ru(CO)L(L1)(η-C5Ph5)][PF6][3; L = PEt3 or P(OMe)3; L1= CO, C2H4, or MeCCMe], and the dicarbonyls [Ru(CO)2L(η-C5Ph5)][PF6][L = PEt3 or P(OMe)3] react with L1, in acetone with ONMe3·2H2O, to give [3; L = L1= PEt3 or P(OMe)3]. Complexes (1) and (2; L = PEt3) react with LiMe in tetrahydrofuran, giving [RuMe(CO)2(η-C5Ph5)](4) and [RuR(CO)(PEt3)(η-C5Ph5)](5; R = Me) respectively, and (5; R = Et, COMe, or CMeCMe2) are prepared from (3; L = PEt3, L1= C2H4) and [NBun4][BH4] or from (3; L = PEt3, L1= CO or MeCCMe) and LiMe. The neutral compounds (1), (2), (4), and (5) undergo diffusion-controlled one-electron oxidation at a platinum bead electrode in CH2Cl2. In most cases the electron-transfer process is fully reversible, but (1), (4), and [FeMe(CO)2(η-C5Ph5)] show only irreversible cyclic voltammetric waves. The chemical oxidation of (2) with [N(C6H4Br-p)3][SbCl6] in CH2Cl2 gives the 17-electron cation (2+), and (5+) have also been characterised in solution after generation from (5) by AgPF6 oxidation. Complexes (1) and (3) undergo diffusion-controlled but chemically irreversible reduction at the platinum electrode; reduction by [Co(η-C5H5)2](i) of [3; L = P(OMe)3, L1= CO] gives a mixture of (4), [Ru{P(O)(OMe)2}(CO)2(η-C5Ph5)], and [RuCl(CO){P(OMe)3}(η-C5Ph5)], (ii) of [3; L = P(OMe)3, L1= MeCCMe] gives [RuH(CO){P(OMe)3}(η-C5Ph5)], and (iii) of (1) gives trans-[{Ru(µ-CO)(CO)(η-C5Ph5)}2](6).

The nitrosonium ion, NO+, and its versatility in transition metal organometallic synthesis

Abstract The versatility of the nitrosonium ion, NO+, in organometallic synthesis is illustrated by its reactions with a variety of transition metal compounds. With the species π-C5H5M(CO)P(C6H5)3, MCo and Rh, NOPF6 reacts in methanol/toluene mixtures to give [π-C5H5M(NO)P(C6H5)3]PF6. When MIr, however, protonation takes place to give the hydride [π-C5H5Ir(CO)P(C6H5)3H]PF6. Halogen-containing organometallics such as π-C5H5Fe(CO)2I, (π-C5H5)2VCl2 and Mn(CO)5Br react with NOPF6 in acetonitrile to give the complexes [π-C5H5Fe(CO)2(CH3CN)]PF6, [(π-C5H5)2V(CH3CN)2][PF6]2 and [Mn(CO)5(CH3CN)]PF6 in which the solvent has replaced the halide ligands. Finally NO+ reacts as a one-electron oxidising agent towards (π-C5H5)2Fe and [π-C5H5Fe(CO)SCH3]2 giving (π-C5H5)2Fe+ and [π-C5H5Fe(CO)SCH3]2+ respectively. Reasons for the formation of the different types of products are discussed.

Synthesis of the 17-electron cations [FeL(L′)(NO)2]+(L, L′= PPh3, OPPh3): structure and bonding in four-co-ordinate metal dinitrosyls, and implications for the identity of paramagnetic iron dinitrosyl complex catalysts

The complex [FeL2(NO)2](L = PEt31a, L = PPh31b or L2= dppe 1c) prepared from [{Fe(µ-I)(NO)2}2] and PPh3 or Ph2PCH2CH2PPh2(dppe){in the presence and absence of [Co(cp)2](cp =η5-C5H5) respectively} undergo one-electron oxidation at a platinum electrode in CH2Cl2. The complex [{Fe(µ-dppm)(NO)2}2]2, prepared from [{Fe(µ-I)(NO)2}2] and Ph2PCH2PPh2(dppm) in the presence of [Co(cp)2], undergoes two sequential one-electron oxidations. Complex 1b with [Fe(cp)2]+ gave 1b+, X-ray studies of which show a distorted tetrahedral geometry with near C2v symmetry. Oxidation of 1b leads to substantial lengthening of the Fe–P bonds and changes in the P–Fe–P and N–Fe–N angles. These changes are consistent with significant Fe–P π-bonding character in the singly occupied molecular orbital of 1b+. Cation 1b+ reacts with halide ions, giving [FeX(PPh3)(NO)2](X = Cl or I) and then [FeX2(NO)2]–, and with OPPh3 to give [Fe(OPPh3)(PPh3)(NO)2]+3. X-Ray studies on the last, as its [PF6]– salt, show a distorted tetrahedral geometry; the co-ordination angles at iron approach trigonal bipyramidal with the PPh3 ligand in one apical site and the other apical site vacant. The complex [Fe(OPPh3)2(NO)2]+4+ resulted from the reaction between [{Fe(µ-I)(NO)2}2] and OPPh3 in the presence of TlPF6. An analysis of the ESR spectra of the paramagnetic cations 1b+, 3+ and 4+, together with extended-Huckel MO calculations on models of 1b+ and 3+, suggest that the complex catalysts formed from [{Fe(µ-Cl)(NO)2}2] and Ag+ or Tl+ are also four-co-ordinate 17-electron radicals. A crystallographic database study of four-co-ordinate dinitrosyl complexes of iron and other metals confirms that the N–Fe–N and O ⋯ Fe ⋯ O angles are linearly related. Consideration of these geometric effects, and those resulting from oxidation of 1b, in the light of a model proposed by Summerville and Hoffmann provides insight into the bonding in these and related species.

Syntheses of dinuclear gold(I) ring complexes containing two different bridging ligands. Crystal structure of [Au2{µ-(CH2)2PPh2}(µ-S2CNEt2)]

The reaction of [Au2{µ-(CH2)2PPh2}2] with [Au2(µ-L–L)2]n+[n= 0, L–L = S2CNMe2, S2CNEt2 or S2CN(CH2Ph)2; n= 2, L–L = Ph2PCH2PPh2(dppm), Ph2P(CH2)2PPh2 or Ph2PNHPPh2] led to heterobridged dinuclear complexes [Au2{µ-(CH2)2PPh2}(µ-L–L)]n+(n= 0 or 1). The same complexes can also be obtained by reaction of [N(PPh3)2][(AuCl)2{µ-(CH2)2PPh2}] with the silver compounds [Ag(S2CNMe2)]6 or [Ag2(OClO3)2(dppm)3] or by reaction of [(AuPPh3)2{µ-(CH2)2PPh2}][ClO4] with [{Au(C6F5)}2(µ-L–L)](L–L = diphosphines or o-Ph2PC5H4N). The structure of [Au2{µ-(CH2)2PPh2}(µ-S2CNEt2)] has been established by X-ray crystallography. Two molecules are bonded through an intermolecular gold–gold interaction, thus forming a linear chain of four gold atoms with Au–Au (intramolecular) 2.867, 2.868, (intermolecular) 2.984 A.

Redox-induced κ2–κ3 isomerisation in rhodium hydrotris(3,5-dimethylpyrazolyl)borate chemistry: the stabilisation of square-pyramidal rhodium(II)

One-electron oxidation of the square-planar, 16-electron complex [Rh(CO)(PPh3)(κ2-Tp′)] with [FeCp2][PF6] gives the square-pyramidal RhII complex [Rh(CO)(PPh3)(κ3-Tp′)][PF6] in which the third pyrazolyl group of Tp′ is N-bound in the axial position by a three-electron two-centre bond (Rh–Naxial 0.13 A longer than Rh–Nbasal).

Activation of µ-alkylidene ligands through oxidation–deprotonation: a new synthesis of µ-methyne, and is hydrogenation to µ-methyl

A new method of activating µ-alkylidene complexes is described, involving oxidation to dications followed by deprotonation, so that µ-CH2 is converted to µ-CHCH2+; the mono-cationic products react with nucleophiles to produce derivatives of the original µ-alkylidene, while µ-CH+ yields µ-CH3+ readily under pressure of hydrogen.

The reversible one-electron oxidation of arenechromium-dicarbonylacetylene complexes

Abstract (C6Me6−nHn)Cr(CO)2 (acetylene), n = 0 and 1; acetylene = PhCCPh and p-MeOC6H4CCC6H4OMe, are reversibly oxidised to the corresponding monocations by NO+, Ag+ or I2. Electrochemical data for the oxidation process, and the ESR spectra of the resulting cations, are reported.