Photolysis of CpRe(CO)2(N2) in cyclopentane or 2,2-dimethylbutane with a UV lamp via a quartz fibre inserted into the NMR probe allows generation of CpRe(CO)2(cyclopentane) and CpRe(CO)2(2,2-dimethylbutane). The latter is observed in three isomeric forms according to the site of co-ordination to the rhenium. The major isomer, CpRe(CO)2(2,2-dimethylbutane-η2-C1,H1), exhibits a 1H NMR resonance for the co-ordinated hydrogen at δ = −2.19 with 1JC–H = 118 Hz. The photochemistry of Cp‡Re(CO)2(N2) (Cp‡ = η5-1,2-C5H3(tBu)2) in alkane solution is also reported. Two new organometallic alkane complexes, Cp‡Re(CO)2(alkane) (alkane = cyclopentane, n-heptane) have been characterized by IR spectroscopy following irradiation of Cp‡Re(CO)2(N2) and their rate constants for reaction with CO have been determined. The reaction with cyclopentane has also been studied by NMR spectroscopy at 190 K with in situ laser irradiation at 355 nm. Cp‡Re(CO)2(c-C5H10) is shown to exhibit the characteristic features of an alkane complex in the NMR spectrum, viz. a large isotopic shift of the 1H resonance at δ = −2.44 upon partial deuteration of the alkane (Δδ = 1.77 ppm), a large 1JC–H (114 Hz) and a large negative 13C chemical shift (δ = −33.8). We find no evidence for CO loss or agostic interactions of the t-butyl groups under these conditions. Cp‡Re(CO)2(alkane) has a slightly shorter lifetime (ca. 5x) than CpRe(CO)2(alkane) for a given alkane. Photolysis of CpRe(CO)2(N2) to form the organometallic alkane complex occurs with a much higher yield than for CpRe(CO)3. Efficient photo-ejection of N2 from Cp‡Re(CO)2(N2) is observed upon either 266 or 355 nm laser irradiation. A dinitrogen precursor allows for the use of longer wavelength irradiation and the generation of a higher concentration of the alkane complex following each laser pulse.

The tethering of a substrate analogue to a covalently attached luminophore may give rise to a probe for reporting enzyme activity spectrofluorometrically. The overall design incorporates a water-soluble porphyrin luminophore, a substrate analogue and a planar conjugated bridge of the appropriate length designed to bind in the substrate-access channel of xanthine oxidase (XO). 5,10,15-Tris(N-methyl-4-pyridiniumyl)-20-phenyl porphyrins was functionalised at the 4-position of the phenyl group with amide-linked 2-methoxy-benzamide groups, [(2-methoxy-4-amino-phenylcarbonyl)-amino] or [(2-methoxy-4-[(pyridine-4-carbonyl)-amino]-phenylcarbonyl)-amino]. The products were isolated as free base or zinc porphyrins with chloride or hexafluorophosphate counterions and characterised by optical emission and absorption in addition to other spectroscopic methods. Binding studies of bovine XO to the zinc porphyrin trichloride derivatives with the above linkers were used to determine the IC50 of 81 and 113 μM and Ki values of 4.6 and 6.5 μM, respectively. Furthermore, addition of XO to an aqueous solution of the products caused quenching of the porphyrin emission and a red shift in the absorption spectrum.

Metal fluoride complexes that are extremely sensitive to air and water have been characterized by liquid injection field desorption/ionization (LIFDI) mass spectrometry. Dilute solutions of fluoride complexes of nickel, rhodium, titanium, zirconium and ruthenium in toluene and tetrahydrofuran were examined by LIFDI methods on a time-of-flight mass spectrometer. All the spectra of nickel, titanium and zirconium complexes exhibited the molecular ion as base peak. The ruthenium and rhodium complexes showed [M−HF]+ as base peaks but the molecular ions were easily detected. The nickel complexes do not provide useful mass spectra by EI or ESI methods. Only the titanium and zirconium species showed evidence of the fluoride ligands in the ESI spectra. Two new nickel fluoride complexes are formed by C–F activation reactions with 2,3,5,6-tetrafluoro-4-dimethylaminopyridine and 2,3,5,6-tetrafluoro-4-methoxypyridine yielding trans-NiF{2-C5NF3(4-NMe2)}(PEt3)2 and trans-NiF{2-C5NF3(4-OMe)}(PEt3)2, respectively. The crystal structure of trans-NiF{2-C5NF3(4-NMe2)}(PEt3)2 shows typical square planar coordination at nickel with an Ni–F distance of 1.8521(9) Å.Metal fluoride complexes of nickel, rhodium, ruthenium, titanium and zirconium have been characterized by liquid injection field desorption/ionization (LIFDI) mass spectrometry. Most show the molecular ion as base peak. Commoner ionization methods give very poor results by comparison.

Density functional theory is used to explore the origins of the chemoselectivity and regioselectivity of activation of C−F bonds in pentafluoropyridine with [Ni(PR3)2] species. Experimentally, Ni-fluoride species are observed and activation occurs preferentially at the 2-position (i.e., the C−F bond ortho to the pyridyl nitrogen). This is in marked contrast to related platinum reagents, which form Pt-alkyl species featuring fluorophosphine ligands with activation occurring exclusively at the 4-position. Using a model nickel complex, [Ni(PMe3)2], computed potential energy surfaces reveal two distinct types of reaction pathways: conventional oxidative addition and phosphine-assisted C−F bond activation. In the latter, the activated fluorine is transferred first to the phosphine ligand before migrating to the metal center. The phosphine-assisted routes lie substantially above their oxidative addition counterparts unless activation occurs at the 2-position, where coordination of the pyridyl nitrogen stabilizes both the metallophosphorane intermediate and the preceding transition state. The result is a lowering of the barrier such that the phosphine-assisted route becomes competitive with conventional oxidative addition. This “neighboring group acceleration” is unique to the phosphine-assisted pathway and, moreover, is unique to activation at the 2-position because it depends on the ability of the nitrogen to participate in a benzyne-like, pyridin-1,2-diyl coordination mode.

Significant Rh–NH π-bonding in formally 16-electron (η5-C5Me5)Rh(XNC6H4NX′) (X, X′ = H or Ts) is shown by structural features and by DFT calculations; (η5-C5Me5)Rh(TsNC6H4NH) is the fastest transfer hydrogenation catalyst of the three complexes and generates a formate complex under catalytic conditions.

Short wavelength photolysis of (Tp)Re(CO)3 (Tp = tris(pyrazol-1-yl)borate) at low-temperature in cyclopentane yielded (Tp)Re(CO)2(cyclopentane), an alkane complex with three nitrogen ligands that was characterised by NMR spectroscopy.

The reactivity, structures, and NMR spectroscopy of a series of compounds relevant to asymmetric transfer hydrogenation, of general formula Cp*RhCl(S,S-4-RC6H4SO2NCHPhCHPhNH2) (Cp* = η5-C5Me5, S,S-2a R = Me, S,S-2b R = tBu, S,S-2c R = F), have been studied. 1H/15N HMQC NMR spectra of 2a−2c were recorded with 15N in natural abundance making use of the coupling to the C5Me5 protons; the coupling constants JRhN were ca. 15 and 20 Hz for the amino and amido nitrogens, respectively. 1H/103Rh NMR spectra of 2a and 2c were recorded similarly. The chloride ligand in S,S-2a has been shown to be very labile; reaction with CO afforded the cationic complex [Cp*Rh(CO){C(O)N(Ts)CHPhCHPhNH2}][Cl] (3a) as a mixture of diastereomers, S,S,RRh and S,S,SRh, with opposite chirality at Rh; reaction with tBuNC gave [Cp*Rh(CNtBu)(S,S-TsCHPhCHPhNH2)][PF6] (4a), and reactions with LiBr and KI gave Cp*RhBr(S,S-TsNCHPhCHPhNH2) (6a) and Cp*RhI(S,S-TsNCHPhCHPhNH2) (7a), respectively. Complexes S,S-2c, S,S-6a, and S,S-7a have been characterized by X-ray crystallography; the amino N−Rh bond is significantly shorter than the amido N−Rh bond in all cases (difference Δr 0.058(2), 0.085(6), and 0.046(4) Å, respectively), and the complexes all possess intramolecular NH···X (X = Cl, Br, I) hydrogen bonds. The reaction of 2a with formic acid results in complete displacement of the chelating ligand and the formation of dinuclear [{Cp*Rh}2(μ-H)(μ-Cl)(μ-HCO2)][BPh4] (5a), which was also characterized crystallographically. Reaction of 2c with AgOTf resulted in the formation of [Cp*Rh(OH2)(4-FC6H4SO2NCHPhCHPhNH2)][OTf] ([8c·H2O][OTf]) or [Cp*Rh(4-FC6H4SO2NCHPhCHPhNH2)]2[OTf]2 ([8c]2[OTf]2) depending upon the conditions employed. [8c·H2O][OTf] was characterized by X-ray crystallography, and the structure showed that both CHPh centers in the ligand had been racemized, converting the S,S isomer of the starting material into a mixture of both R,R and S,S isomers.

The synthesis is reported of a series of metalloporphyrins (and the corresponding free-base porphyrin), mono-meso-substituted with a bipyridyl groupvia an amide link at the 4-position of one phenyl group: [Re(CO)3(Pic)Bpy-MTPP][OTf], where M = Mg, Zn, Pd or 2H, Pic = 3-picoline, Bpy = 2,2′-bipyridine, TPP = tetraphenylporphyrin. The photochemical reactions of the assemblies with the sacrificial electron donor triethylamine have been investigated by IR spectroscopy and compared to the behaviour of analogues of the type Bpy-MTPP without rhenium. Selective long-wavelength irradiation of the metalloporphyrin unit in the presence of excess picoline leads to reduction at the rhenium bipyridine centre. In the absence of 3-picoline, the latter is not reduced, but substituted by added halide or by the THF solvent. Mechanistic analysis highlights the differences between the zinc and magnesium chelate on the one hand and the palladium porphyrin on the other. The free-base assembly, [Re(CO)3(Pic)Bpy-H2TPP][OTf] is unreactive. The zinc and magnesium porphyrin assemblies initially coordinate Et3N before undergoing photo-induced inner-sphere electron transfer from the triethylamine to form a charge-shifted excited state of the assembly. In contrast, the palladium-based dyad reacts via outer-sphere reductive quenching of a porphyrin-based excited state. The substitution products are postulated to form by a mechanism involving an electron-transfer chain.

The C–F bond activation of fluoropyridines by [Rh(SiPh3)(PMe3)3] afforded Rh(I) fluoropyridyl complexes of the type [Rh(ArF)(PMe3)3] with concomitant formation of fluorotriphenylsilane; subsequent treatment with bis-catecholatodiboron yielded fac-[Rh(Bcat)3(PMe3)3] and the free fluoropyridyl boronate esters (ArFBcat).

Low temperature in situ UV irradiation of [(η5-C5H5)Co(C2H4)2] in the presence of silanes enables the characterisation of unstable fluxional Co(III) silyl hydride complexes [(η5-C5H5)Co(SiR3)(H)(C2H4)] (SiR3 = SiEt3, SiMe3 or SiHEt2) by NMR spectroscopy; the reaction of [Co(η5-C5H5)(C2H4)2] with HSiR3 proceeds thermally to reach an equilibrium when SiR3 = Si(OMe)3 or SiClMePh.

The reaction of Ni(COD)2 (COD = 1,5-cyclooctadiene) with triethylphosphine and pentafluoropyridine in hexane has been shown previously to yield trans-[NiF(2-C5NF4)(PEt3)2] (1a) with a preference for reaction at the 2-position of the heteroaromatic. The corresponding reaction with 2,3,5,6-tetrafluoropyridine was shown to yield trans-[NiF(2-C5NF3H)(PEt3)2] (1b). In this paper, we show that reaction of Ni(COD)2 with triethylphosphine and pentafluoropyridine in THF yields a mixture of 1a and 1b. Competition reactions of Ni(COD)2 with triethylphosphine in the presence of mixtures of heteroaromatics in hexane reveal a kinetic preference of k(pentafluoropyridine) : k(2,3,5,6-tetrafluoropyridine) = 5.4 : 1. Treatment of 1a and 1b with Me3SiN3 affords trans-[Ni(N3)(2-C5NF4)(PEt3)2] (2a) and trans-[Ni(N3)(2-C5NHF3)(PEt3)2] (2b), respectively. The complex trans-[Ni(NCO)(2-C5NHF3)(PEt3)2] (3b) is obtained on reaction of 1b with Me3SiNCO and by photolysis of 2b under CO, while trans-[Ni(η1-CCPh)(2-C5NF4)(PEt3)2] (4a) is obtained by reaction of phenylacetylene with 1a. Addition of KCN, KI and NaOAc to complex 1a affords trans-[Ni(X)(2-C5NF4)(PEt3)2] (5a X = CN, 6a X = I, 7a X = OAc), respectively. The PEt3 groups of complex 1a are readily replaced by addition of 1,2-bis(dicyclohexylphosphino)ethane (dcpe) to produce [NiF(2-C5F4N)(dcpe)] (8a). Addition of dcpe to trans-[Ni(OTf)(2-C5F4N)(PEt3)2] (10a), however, yields the salt [Ni(2-C5F4N)(dcpe)(PEt3)](OTf) (9a) by substitution of only one PEt3 and displacement of the triflate ligand. The structures of 2b, 4a, 7a and 8a were determined by X-ray crystallography. The influence of different ancillary ligands on the bond lengths and angles of square-planar nickel structures with polyfluoropyridyl ligands is analysed.

The compound CpRh(C2H3CO2tBu)21 has been synthesised as a mixture of two pairs of interconverting isomers which differ in the relative orientations of the alkene substituents. The four isomers have been fully characterised by NMR spectroscopy. When complex 1 is photolysed in the presence of a silane, HSiR2R′ [R2R′ = Et3, Me3, HEt2, (OMe)3 and Me2Cl] the corresponding Si–H oxidative addition products CpRh(SiR2R′)(H)(C2H3CO2tBu) and CpRh(H)2(SiR2R′)2 are formed. The Rh(III) complexes CpRh(SiR2R′)(H)(C2H3CO2tBu) exist in two isomeric forms of comparable energy which interconvert in an intramolecular process that does not involve a reversible [1,3] hydride or [1,3] silyl migration. The hydride 1H NMR resonances for these species consequently broaden before coalescing into a single peak. For R2R′ = Et3, the activation parameters for interchange from the major to minor isomer were ΔH‡ = 60.2 ± 2 kJ mol−1 and ΔS‡ = 8 ± 9 J mol−1 K−1, while for R2R′ = Me3 and Et2H, ΔH‡ = 61.5 ± 1 kJ mol−1, ΔS‡ = 6 ± 5 J mol−1 K−1, and ΔH‡ = 61.8 ± 3 kJ mol−1, ΔS‡ = 12 ± 9 J mol−1 K−1 respectively for conversion from the major isomer to the minor. For these complexes an η2-Rh–H–Si transition state or intermediate is consistent with the evidence. When R2R′ = (OMe)3 and Me2Cl the change in appearance of the hydride resonances is more complex, with the activation parameters for interchange from the major to minor isomer for the former species being ΔH‡ = 78.3 ± 2 kJ mol−1 and ΔS‡ = 30 ± 7 J mol−1 K−1 while for Me2Cl the barrier proved too high to measure before decomposition occurred. The complex spectral changes could be simulated when a discrete η2-Rh–H–Si intermediate was involved in the isomer interconversion process and hence silane rotation in all these systems is proposed to involve two isomers of CpRh(η2-HSiR2R′)(C2H3CO2tBu).

A series of carbene complexes RhCl(CR′2)(PR3)2 (R = Ph, Tol, Me, R′ = Ph and Tol) have been synthesised through direct reaction of photochemically generated free diarylcarbene with RhCl(CO)(PR3)2. This route to carbene complexes demonstrates the reactivity of simple diarylcarbenes towards transition metal complexes. The reactivity of some of these complexes towards H2, C2H4 and Et3SiH has been investigated.

DFT methods are used to quantify the relationship between M–C and H–C bond energies; for MLn = Re(η5-C5H5)(CO)2H and fluorinated aryl ligands, theoretical and experimental investigations of ortho-fluorine substitution indicate a much larger increase in the M–C than in the H–C bond energy, so stabilising C–H activation products.

The fluoride-bridged ruthenium dimers [Ru2(μ-F)3(PR3)6][F(HF)n] (R = Et, Pr, Bu; n ≈ 3) were synthesised by the reactions of the cis-[RuH2(PR3)4] complexes with NEt3·3HF in THF; the crystal structure of [Ru2(μ-F)3(PEt3)6]OTf, formed by subsequent reaction with NH4OTf, reveals Ru–F distances in the range 2.132(2)–2.170(2) Å and Ru–F–Ru angles in the range 91.72(7)–93.02(7)°.

Density functional calculations have been used to examine the reaction of {CpRe(CO)2} with fluorobenzenes C6FnH6−n (n = 0–5). Two classes of product have been observed experimentally (using Cp or Cp*): (a) coordination of the arene in an η2 fashion and (b) C–H activation to form a hydrido–aryl complex. Increasing the number of fluorines on the arene ring was shown to favour C–H activation. The thermodynamic and kinetic (reaction path) aspects of these transformations have been examined with DFT (B3PW91) calculations. For a given arene, the rhenium moiety is shown to exhibit the following order of thermodynamic preference for coordination: HCCH site > HCCF site > FCCF site. Binding energies to the different arenes do not follow a clear trend and span ca. 20 kJ mol−1. The Re–C bond energies in CpRe(CO)(H)(C6FnH5−n) span 55 kJ mol−1. Calculated structural parameters agree with the crystal structure of coordination of C6H6 and C6F6. Likewise the binding energy of C6H6 is in good agreement with experimental data. The calculated free energy difference between CpRe(CO)2(η2-C6FnH6−n) and CpRe(CO)2(H)(C6FnH5−n) shows that preference for the hydrido–aryl complex is determined principally by the bond dissociation energy of the C–H bond of the free arene. The binding energy to the η2-arene appears to be only a secondary factor. Three families of complexes are apparent. If there is no F on the carbon ortho to the Re–C bond that is formed, the η2-arene complex is energetically preferred. If there is one F at the ortho position, the energies of the products are similar. In the case of two ortho F substituents, the product of oxidative addition is significantly favoured. In agreement with the calculations, experimental evidence shows that benzene only coordinates to Cp*Re(CO)2, 1,4-C6F2H4 gives a mixture of products and 1,3-C6F2H4 gives only the hydrido–aryl complex. The arene with the stronger C–H bond is the one which gives more oxidative addition product because the Re–C bond energy increases with F substitution (and in particular with ortho F) more than twice as fast as the C–H bond dissociation energy. The reaction path for the overall transformation has been determined. The σ C–H complex is identified as an intermediate on the pathway for the oxidative addition. The initial product of oxidative addition is the cis hydrido–aryl isomer which subsequently isomerizes to the trans isomer. The rate determining step has been found to be the cis–trans isomerisation process and not the oxidation addition step. The cis–trans isomerisation proceeds via an unconventional concerted motion of H and the two COs. The variation of the Re–C bond energy is the dominant factor in determining the changes in the energy barrier between the different fluoroarenes, resulting in strong correlation between the thermodynamics and kinetics of reaction. The activation barriers are therefore also grouped in three families (0 F ortho, 1 F ortho, 2 F ortho).

The photochemical and electrochemical properties of a Zn-porphyrin appended rhenium(I) tricarbonyl bipyridine 3-Me-pyridine complex have been investigated; visible-light sensitisation of electron transfer results in ligand substitution at a site remote from the chromophore.

The cross-coupling reaction of pentafluoropyridine with tributyl(vinyl)tin affording 2-vinyltetrafluoropyridine by activation of a carbon–fluorine bond is catalysed by [NiF(2-C5NF4)(PEt3)2]; a similar reaction is observed with 2,3,5,6-tetrafluoropyridine.

UV irradiation of [(η5-C5Me5)Re(CO)2N2] in neat 1,4-C6H4F2 generates a mixture of the C–H activation product trans-[(η5-C5Me5)Re(CO)2(2,5-C6H3F2)H] 1a and the η2-arene complex [(η5-C5Me5)Re(CO)2(2,3-η2-1,4-C6H4F2)] 2a, identified on the basis of their IR and NMR spectra. Reaction of the mixture with CHBr3 allowed the isolation of trans-[(η5-C5Me5)Re(CO)2(2,5-C6H3F2)Br] 1a–Br; subsequent reaction with LiBEt3H followed by HCl at low temperature provided an independent route to 1a free of 2a. Nevertheless, complex 1a converts to 2a above 213 K. NOESY/EXSY spectroscopy of mixtures of 1a and 2a at low temperature shows that a conformer of 2a is populated at low temperature in which the hydrogen atoms on the coordinated carbons point towards the η5-C5Me5 ring. Rapid exchange occurs between the hydrogen atoms on the coordinated carbons in 2a and those on the uncoordinated carbons via an unusual [1,4]-metallotropic shift with ΔH‡ = 59 ± 8 kJ mol−1 and ΔS‡ ≈ 0. There is no evidence from NMR spectroscopy for intermolecular exchange between 1a and 2a or between these complexes and free 1,4-C6H4F2. It is postulated that photolysis initially generates 2a which is converted to 1a in a secondary photochemical step. The ratio of 1a to 2a is controlled by the photochemical conditions and the thermal conversion of 1a to 2a. Thermal reaction of a mixture of 1a and 2a yields two dimers, [(η5-C5Me5)2Re2(CO)5)] and [{(η5-C5Me5)Re(CO)2}2(μ-2,3-η2-4,5-η2-1,4-C6H4F2)] 3. Complex 3 was isolated in low yield and shown to contain the first example of coordination to a CHCF bond as well as a CHCH bond. DFT calculations were carried out on [(η5-C5H5)Re(CO)2(2,5-C6H3F2)H] 1b, [(η5-C5H5)Re(CO)2(2,3-η2-1,4-C6H4F2)] 2b and [(η5-C5H5)Re(CO)2(1,2-η2-1,4-C6H4F2)] 4b. Two minima were located for each of 2b and 4b corresponding to the two conformations of the arene ring with respect to the cyclopentadienyl group. The most stable complex was 2b, followed by 1b and then by 4b, successfully reproducing the stability of 2a compared to 1a and the absence of experimental evidence for 4a. Theoretical investigations of the [1,4]-metallotropic shift show that it occurs via three sequential [1,2]-shifts. The rate determining step is predicted to be the shift across the C–F moiety. In the transition states, the rhenium atom has a short bond to a single carbon atom and extended bonds to two neighbouring carbon atoms.

Bifluoride complexes, trans-[Ru(depe)2H(FHF)] (1), trans-[Ru(dppe)2H(FHF)] (2), trans-[Ru(dppp)2H(FHF)] (3) and cis-[Ru(PMe3)4(FHF)2] (4) (depe = Et2PCH2CH2PEt2, dppe = Ph2PCH2CH2PPh2, dppp = Ph2PCH2CH2CH2PPh2) were synthesised from the reactions of the corresponding cis-dihydride complexes with NEt3·3HF in THF. The characteristic features of the low temperature NMR spectra of the bifluoride complexes include 19F resonances at ca.δ −300 for the proximal fluorine and ca.δ −165 for the distal fluorine. The acidic protons resonate at ca.δ 13. The value of J(HF) for the distal fluorine lies in the range 300–400 Hz. The bifluoride ligands exhibit characteristic vibrations at ca. 2300 cm−1 and ca. 2430 cm−1 in the IR spectrum. All the complexes exhibit dynamic exchange processes, probably due to dissociation of FHF−. In addition, complex 3 undergoes a ring flipping process that is suppressed at low temperature. The X-ray crystal structure of 3 has been obtained. The bifluoride ligand is disordered over two positions about the inversion centre. The Ru–F distance is 2.351(5) Å and the F⋯F distance is 2.290(8) Å, the Ru–F⋯F angle is 149.7°. The X-ray crystal structure for 4 reveals that the Ru–F distances are 2.149(5) Å and 2.150(4) Å, the F⋯F bond lengths are 2.323(8) Å and 2.329(8) Å, with Ru–F⋯F angles of 128.5(3)° and 138.4(3)°. The two bifluoride ligands are cis to each other. Reaction of 1 and 3 with [NMe4]F yields trans-[Ru(depe)2(H)F] 5 and trans-[Ru(dppp)2(H)F] 6. Reaction of 2 with Me3SiX (X = N3, OTf) yields trans-[Ru(dppe)2(H)N3] and [Ru(dppe)2(H)]OTf. Reactions with several halo-organic compounds yields trans-[Ru(dppe)2(H)X] (X = Cl, Br and I). The organic products from CH3I, CH3COCl and C6H5COCl were identified as CH3F, CH3COF and C6H5COF respectively.

Reaction of [Ni(COD)2] with PEt3 and octafluoronaphthalene yielded the complex [Ni(η2-1,2-C10F8)(PEt3)2] 1, which was converted thermally into the C–F activation product trans-[NiF(2-C10F7)(PEt3)2] 2. The crystal structure of 1 shows asymmetric η2 coordination with significant distortions of the naphthalene unit compared to the “ free” ligand; DFT calculations reproduce the principal features of the geometry.

cis-[Ru(PMe3)4(H)2] (1) reacts by two distinct photochemical pathways resulting in the formation of [Ru(PMe3)4] and [Ru(PMe3)3(H)2]; derivatives of these intermediates are generated in the presence of CO and Ph2SiH2.

Treatment of trans-[NiF(2-C5NF4)(PEt3)2] (C5NF4 = tetrafluoropyridyl) (1) with HCl effects the formation of the air stable chloride complex trans-[NiCl(2-C5NF4)(PEt3)2] (2). The reaction of 2 with excess HCl slowly yields 2,3,4,5-tetrafluoropyridine (4). On reaction of 4 with [Ni(COD)(PEt3)2], the C–F activation product trans-[NiF(2-C5NF3H)(PEt3)2] (5) is formed instantly. The bifluoride compound trans-[Ni(FHF)(2-C5NF4)(PEt3)2] (6) is obtained on treatment of 1 with Et3N·3HF. Reaction of 2 with HBF4 yields the binuclear complex [NiCl{μ-κ2(C,N)-(2-C5NF4)}(PEt3)]2 (7). The X-ray crystal structure of 7 reveals a “butterfly”-shaped dimeric complex with square-planar coordination at both nickel atoms, with Ni–N distances of 1.965(4) and 1.955(4) Å and Ni–C distances of 1.884(5) and 1.875(5) Å. Treatment of 1 with BF3·OEt2 in the presence of acetonitrile yields the cationic compound trans-[Ni(2-C5NF4)(NCMe)(PEt3)2]BF4 (8), while reaction of trans-[Ni(OTf)(2-C5NF4)(PEt3)2] (3) with NaBAr′4 and acetonitrile gives trans-[Ni(2-C5NF4)(NCMe)(PEt3)2]BAr′4 (9) [Ar′ = 3,5-C6H3(CF3)2]. The studies reported in this paper provide methods for the synthesis of tetrafluoropyridines substituted in the 2-position and demonstrate the behaviour of nickel derivatives with Brønsted acids and the Lewis acid BF3.

Photolysis of CpRe(CO)2(N2) in cyclopentane or 2,2-dimethylbutane with a UV lamp via a quartz fibre inserted into the NMR probe allows generation of CpRe(CO)2(cyclopentane) and CpRe(CO)2(2,2-dimethylbutane). The latter is observed in three isomeric forms according to the site of co-ordination to the rhenium. The major isomer, CpRe(CO)2(2,2-dimethylbutane-η2-C1,H1), exhibits a 1H NMR resonance for the co-ordinated hydrogen at δ = −2.19 with 1JC–H = 118 Hz. The photochemistry of Cp‡Re(CO)2(N2) (Cp‡ = η5-1,2-C5H3(tBu)2) in alkane solution is also reported. Two new organometallic alkane complexes, Cp‡Re(CO)2(alkane) (alkane = cyclopentane, n-heptane) have been characterized by IR spectroscopy following irradiation of Cp‡Re(CO)2(N2) and their rate constants for reaction with CO have been determined. The reaction with cyclopentane has also been studied by NMR spectroscopy at 190 K with in situ laser irradiation at 355 nm. Cp‡Re(CO)2(c-C5H10) is shown to exhibit the characteristic features of an alkane complex in the NMR spectrum, viz. a large isotopic shift of the 1H resonance at δ = −2.44 upon partial deuteration of the alkane (Δδ = 1.77 ppm), a large 1JC–H (114 Hz) and a large negative 13C chemical shift (δ = −33.8). We find no evidence for CO loss or agostic interactions of the t-butyl groups under these conditions. Cp‡Re(CO)2(alkane) has a slightly shorter lifetime (ca. 5x) than CpRe(CO)2(alkane) for a given alkane. Photolysis of CpRe(CO)2(N2) to form the organometallic alkane complex occurs with a much higher yield than for CpRe(CO)3. Efficient photo-ejection of N2 from Cp‡Re(CO)2(N2) is observed upon either 266 or 355 nm laser irradiation. A dinitrogen precursor allows for the use of longer wavelength irradiation and the generation of a higher concentration of the alkane complex following each laser pulse.

The synthesis is reported of a series of metalloporphyrins (and the corresponding free-base porphyrin), mono-meso-substituted with a bipyridyl groupvia an amide link at the 4-position of one phenyl group: [Re(CO)3(Pic)Bpy-MTPP][OTf], where M = Mg, Zn, Pd or 2H, Pic = 3-picoline, Bpy = 2,2′-bipyridine, TPP = tetraphenylporphyrin. The photochemical reactions of the assemblies with the sacrificial electron donor triethylamine have been investigated by IR spectroscopy and compared to the behaviour of analogues of the type Bpy-MTPP without rhenium. Selective long-wavelength irradiation of the metalloporphyrin unit in the presence of excess picoline leads to reduction at the rhenium bipyridine centre. In the absence of 3-picoline, the latter is not reduced, but substituted by added halide or by the THF solvent. Mechanistic analysis highlights the differences between the zinc and magnesium chelate on the one hand and the palladium porphyrin on the other. The free-base assembly, [Re(CO)3(Pic)Bpy-H2TPP][OTf] is unreactive. The zinc and magnesium porphyrin assemblies initially coordinate Et3N before undergoing photo-induced inner-sphere electron transfer from the triethylamine to form a charge-shifted excited state of the assembly. In contrast, the palladium-based dyad reacts via outer-sphere reductive quenching of a porphyrin-based excited state. The substitution products are postulated to form by a mechanism involving an electron-transfer chain.

Significant Rh–NH π-bonding in formally 16-electron (η5-C5Me5)Rh(XNC6H4NX′) (X, X′ = H or Ts) is shown by structural features and by DFT calculations; (η5-C5Me5)Rh(TsNC6H4NH) is the fastest transfer hydrogenation catalyst of the three complexes and generates a formate complex under catalytic conditions.

The C–F bond activation of fluoropyridines by [Rh(SiPh3)(PMe3)3] afforded Rh(I) fluoropyridyl complexes of the type [Rh(ArF)(PMe3)3] with concomitant formation of fluorotriphenylsilane; subsequent treatment with bis-catecholatodiboron yielded fac-[Rh(Bcat)3(PMe3)3] and the free fluoropyridyl boronate esters (ArFBcat).

Low temperature in situ UV irradiation of [(η5-C5H5)Co(C2H4)2] in the presence of silanes enables the characterisation of unstable fluxional Co(III) silyl hydride complexes [(η5-C5H5)Co(SiR3)(H)(C2H4)] (SiR3 = SiEt3, SiMe3 or SiHEt2) by NMR spectroscopy; the reaction of [Co(η5-C5H5)(C2H4)2] with HSiR3 proceeds thermally to reach an equilibrium when SiR3 = Si(OMe)3 or SiClMePh.