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From the mid-1800s to the late 1960s, conservation by alum salts (KAl(SO4)2·12H2O—potassium aluminium sulphate), using various recipes, was a common method to prevent shrinkage and to strengthen waterlogged archaeological wooden objects. This method was mainly used in Scandinavia. The alum method appears to have also been applied to highly degraded archaeological waterlogged wood in other countries, for example in the U.S and Germany. Today, many of the archaeological wooden objects treated with alum show extreme deterioration and very low pH, which are attributed to the effects of the alum-treatment. This study investigated the extent of the current levels of chemical degradation in wooden objects conserved with alum salts at different points in time (1880s, 1930s and 1905–13) in order to understand their current condition and whether extent of degradation was in any way related to time of treatment, in an attempt to understand the rate of degradation. It was also an opportunity to compare the chemical state of preservation of alum-treated wood from different collections, as only the Oseberg collection has been intensively studied in this way up until now. Samples from historical wooden objects from the following collections were investigated and compared: the Dejbjerg collection (National Museum of Denmark in Copenhagen); the Oseberg collection (Museum of Cultural History, Oslo, Norway); the Glimmingehus collection (Swedish History Museum, Sweden). Analyses of lignocellulosic polymers and of inorganic compounds were undertaken to evaluate the chemical preservation of the wooden objects. The investigations were performed using a multi-analytical approach which consisted of: pH measurements, analytical pyrolysis (Py-GC/MS), X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS). It was possible to link the extent of degradation with time, on a general level but we found a great variability in the state of preservation of the wood also within the same collection. It is clear, however that alum-treated wood is more degraded than archaeological wood not treated with alum.

Carbon dioxide can play a vital role as a sustainable feedstock for chemical synthesis. To be viable, the employed protocol should be as mild as possible. Herein we report a methodology to incorporate CO2 into primary, secondary, aromatic or alkyl amines catalysed by a Rh(I) complex bearing a perimidine-based NHC/phosphine pincer ligand. The periminide-based ligand belongs to a class of 6-membered NHC ligand accessed through chelate-assisted double C–H activation. N-Formylation and -methylation of amines were performed using a balloon of CO2, and phenylsilane as the reducing agent. Product selectivity between formylated and methylated products was tuned by changing the solvent, reaction temperature and the quantity of phenylsilane used. Medium to excellent conversions, as well as tolerance to a range of functional groups, were achieved. Stoichiometric reactions with reactants employed in catalysis and time course studies suggested that formylation and methylation reactions of interest begin with hydrosilylation of CO2 followed by reaction with amine substrates.

The salt elimination reactions of [NEt4][Mo(CSe)(CO)2(Tp*)] ([NEt4][2], Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with a range of metal halide complexes (ClMLn) have been investigated as a possible route to isoselenocarbonyl complexes [Mo(CSeMLn)(CO)2(Tp*)]. Thus the reactions of [NEt4][2] with [RuCl(L)2(η-C5R5)] provide molybdenum-ruthenium derivatives [Mo{CSeRu(L)2(η-C5R5)}(CO)2(Tp*)] (L = PPh3, R = H 4, L = CO, R = Me 5), both of which were structurally characterised. The molybdenum-iron derivative [Mo{CSeFe(CO)2(η-C5H5)}(CO)2(Tp*)] (6) was obtained from [NEt4][2] and [FeCl(CO)2(η-C5H5)] however its formulation currently rests on spectroscopic and microanalytical data. The reaction of [NEt4][2] with [RuH(NCMe)(CO)2(PPh3)2]PF6 affords the structurally characterised hydrido-isoselenocarbonyl complex [Mo{CSeRuH(CO)2(PPh3)2}(CO)2(Tp*)] (7) with no indication of coupling of the hydride and selenocarbonyl ligand.

Samples of conserved archaeological wood of different ages, origins, and conservation histories were aged in a climate chamber for seven months, while the humidity alternated between 30% RH for 12 hours and 80% RH for 12 hours at a constant temperature of 30°C. Photographs were taken once every hour, which enabled the creation of a time-lapse movie. Some samples degraded visibly, whereas others were unaffected. Most of the samples were robust and would be able to survive well even in a very poor museum climate. Among the sensitive samples, three types of degradation were identified, namely disintegration, pyrite oxidation, and efflorescence of white crystals. Disintegration was ascribed to dimensional changes caused by the RH alternations in very fragile wood. The white efflorescence was interpreted as the recrystallization of an alum-associated substance, possibly mercallite (KHSO4). The pyrite oxidation was observed as the efflorescence of a thick yellow, grey, and green powder. Characterization of selected samples was performed using X-ray fluorescence spectrometry, X-ray diffraction spectrometry, scanning electron microscopy with energy dispersive X-ray spectroscopy, inductively coupled plasma – optical emission spectroscopy, Fourier transform infrared spectroscopy, ionic conductivity – liquid chromatography, and pyrolysis-gas chromatography-mass spectrometry with in situ silylation using hexamethyldisilazane.

The Viking Age wooden artefacts recovered in the early 1900s from the Oseberg mound (Norway) and treated with alum, are today highly degraded. This is due to the effects of the alum-treatment and the reactivity of alum and alum-derived salts [1]. Some of the artefacts from the Oseberg collection that were treated with alum were also coated with a drying oil: boiled linseed oil. These artefacts appear to be better preserved with respect to those not treated with linseed oil. In order to assess the effect of linseed oil on wood preservation, an alum-treated archaeological wood fragment from the Oseberg collection treated with linseed oil was investigated by three analytical techniques: gas chromatography coupled with mass spectrometry (GC/MS), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and high-performance liquid chromatography coupled to electrospray ionisation and quadrupole time-of-flight mass spectrometry (HPLC-ESI-Q-ToF). These techniques provided important information on the molecular composition and state of preservation of both archaeological wood and aged linseed oil. Py(HMDS)-GC/MS was applied to assess the state of preservation of the main wood components, lignin and polysaccharides, in the presence of linseed oil and alum treatments. GC/MS and HPLC-ESI-Q-ToF were used to perform lipid characterisation and to investigate the lipid degradation and oxidation processes. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and elemental analysis by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDS) were performed to give information on the corresponding inorganic components, particularly the composition and distribution of the alum. Samples taken at different depths from the surface of the archaeological wood fragment were analysed and compared. The results showed that, although the wood was highly depleted of carbohydrates, it was better preserved than previously analysed Oseberg artefacts not treated with linseed oil. Results from GC/MS and HPLC-ESI-Q-ToF suggested that the linseed oil played a mitigating role in terms of wood degradation. The behaviour of the lipid material, which was more oxidized on the wood surface than in the core, was the opposite to that usually encountered in archaeological wood, suggesting a selective oxidation of the linseed oil. This unusual pattern of wood degradation was not mirrored by the inorganic components: alum was found to be more abundant at the surface of the fragment than at depth, as would be expected, but no decomposition products were found. However, the alum appeared to mainly consist of ammonium salt, rather than the potassium alum documented as the treatment material for the Oseberg artefacts.

The Oseberg collection includes the most complete ensemble of wooden remains from the Viking Age. However, since many of the wooden objects were treated with alum in the early 1900s, they now suffer from dramatic conservation issues. A multi-analytical approach was adopted to investigate both the organic and the inorganic components of some selected wood fragments, with the aim of fully characterising the materials and their decomposition products. A particular focus was taken on the differences between the surface and the core of the fragments analysed, and on the correlations between the results obtained by the different techniques, in order to disclose possible interactions between the materials during degradation. In addition to differences in alum concentration and wood alteration between the surface and the core, some decomposition/transformation products of alum, such as mercallite (KHSO 4 ), were identified by FTIR and XRD. Contextual interpretation of the results obtained by ICP-OES elemental analysis of inorganic components and Py(HMDS)-GC/MS characterisation of degraded lignocellulosic materials supported some previous observations about potential relationships between specific metals (Al, Fe, Ca) and wood degradation and enabled new correlations to be highlighted. Although similar degradation patterns were revealed in the investigated objects–depletion of holocellulose, oxidation of lignin and some transformation of alum - a notable variability at the molecular level was highlighted. This is an important factor to be taken into account for the planning of re-treatment strategies of these extremely precious artefacts.

The reaction of HB(NCH2PPh2)2C6H4-1,2 with [OsCl(Ph)(CO)(PPh3)2] affords the boryl pincer complex [OsCl(CO)(PPh3){B(NCH2PPh2)2C6H4}]. This complex, and its ruthenium analogue were observed to undergo various reactions involving substitution of the chloride and triphenylphosphine co-ligands to give new complexes [MCl(CO)(CNC6H2Me3){B(NCH2PPh2)2C6H4}] (M = Ru, Os), [MH(CO)(PPh3){B(NCH2PPh2)2C6H4}] (M = Ru, Os) and [Ru(κ2-S,S′-S2CNEt2)(CO){B(NCH2PPh2)2C6H4}]. The ruthenium complex [RuH(CO)(PPh3){B(NCH2PPh2)2C6H4}] was found to react with carbon disulfide and carbon monoxide to give the complexes [Ru(κ2-S,S′-S2CH)(CO){B(NCH2PPh2)2C6H4}] and [RuH(CO)2{B(NCH2PPh2)2C6H4}], respectively, the latter as an apparently interconverting mixture of cis and trans dicarbonyl isomers.

The heterogeneity and molecular weight of a chitosan of low molecular weight (molar mass) and low degree of acetylation (0.1) for potential use as a consolidant for decayed archaeological wood were examined by sedimentation velocity and sedimentation equilibrium in the analytical ultracentrifuge before and after depolymerisation. Sedimentation velocity before depolymerisation revealed a uniform distribution of sedimentation coefficient with little concentration dependence. SEDFIT-MSTAR analysis revealed a weight average molecular weight Mw of (14.2 ± 1.2) kDa, and polydispersity index of ~ 1.2. Further analysis using MULTISIG revealed a distribution of material between 2 and 20 kDa and consistent with the weight average Mw. Controlled depolymerisation using hydrogen peroxide and ultra-violet radiation in an acetic acid medium reduced this to (4.9 ± 0.7) kDa, with a similar polydispersity. The depolymerised material appears to be within the range that has been predicted to fully penetrate into archaeological wood. The consequences for this finding and the use of the analytical ultracentrifuge in wood conservation strategies are considered.

Alum-treated archaeological woods from the Oseberg collection, excavated and treated in the early 1900s demonstrate an extreme deterioration, only discovered in the past decade. This research was aimed at understanding the characteristics of the naturally aged material through chemical analyses of both organic and inorganic components, in order to provide information for the preservation/conservation of these precious objects. Analytical pyrolysis-gas chromatography/mass spectrometry with in situ silylation using hexamethyldisilazane (Py(HMDS)-GC/MS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) were used to investigate a set of samples of alum-treated archaeological wood and untreated archaeological wood. Sound woods of the same species were also analysed in order to compare the results. Results from Py(HMDS)-GC/MS analyses of alum-treated woods from Oseberg showed an extreme depletion of carbohydrates and a highly deteriorated lignin network. The majority of the lignin had undergone oxidation reactions, illustrated by high relative amounts of acidic pyrolysis products. In particular, p-hydroxy-benzoic acid was detected for the first time as a degradation product of archaeological wood. Results from ICP-AES showed variable concentrations of aluminium and potassium from the alum treatment, as well as iron, copper, zinc and calcium. The extent of oxidation observed by Py(HMDS)-GC/MS appeared to correlate with relative amounts of iron and calcium in the samples, which may suggest that degradation promoted by iron compounds is inhibited in the presence of calcium compounds. The results obtained for a sample of archaeological wood treated with alum salts five years ago showed that chemical deterioration of lignin had already begun, mainly involving depolymerisation reactions, though only a slight increase in oxidation was evident. In addition to increased insight into potential deterioration reactions, occurring in a complex material such as alum-treated archaeological wood, it was possible to relate the degree of chemical degradation of the Oseberg woods to their visual condition (observed with the naked eye).

The reactions of N,N'-bis(phosphinomethyl)dihydroperimidine pro-ligands H2C(NCH2PR2)2C10H6-1,8 (R = Ph 1a, R = Cy 1b) with iridium(i) substrates have been investigated and shown to readily result in chelate-assisted C-H activation processes. The reaction of 1b with [Ir2Cl2(COE)4] (COE = cyclo-octene) affords the 18-electron iridium(iii) dihydrido complex [IrH2Cl{κ3-C,P,P'-C(NCH2PCy2)2C10H6}], which forms [IrHCl2{κ3-C,P,P'-C(NCH2PCy2)2C10H6}] under acidic (HCl) conditions. In contrast, reaction of 1a with [Ir2Cl2(COD)2] (COD = 1,5-cyclo-octadiene) affords the complex [IrCl(COD){κ2-P,P'-H2C(NCH2PPh2)2C10H6}], thermolysis of which affords cyclo-octene and the pincer-NHC complex [IrCl{κ3-C,P,P'-C(NCH2PPh2)2C10H6}]. The reaction of 1a with two equivalents of [Ir2Cl2(COD)2] provides the binuclear complex [Ir2{μ-H2C(NCH2PPh2)2C10H6}Cl2(COD)2] which is also observed to accumulate and then dissipate during the preceding thermolysis. Related binuclear complexes [M2{μ-H2C(NCH2PPh2)2C10H6}Cl4(η-C5Me5)2] (M = Ir, Rh) which obviate C-H activation were similarly synthesised.

Alum-treated wooden artefacts from the Oseberg collection display a great deal of morphological, structural and compositional inhomogeneity. Thus, an in-depth understanding of chemical processes underlying their degradation requires consideration of a variety of local environments. In addition to alum, sources of inorganic compounds include metal parts, corrosion products of which can migrate into the surrounding wood. In order to characterise the inorganic compounds a range of local environments, samples from several locations in a selection of composite objects have been investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and scanning electron microscopy (SEM)-energy dispersive X-ray spectroscopy (EDS). We have found that corrosion of iron rods used in reconstruction has formed iron(II) sulfates, which have migrated into the alum-treated wood to form sulfates containing combinations of potassium, aluminium, iron(II) and iron(III) cations. Reactions of alum were also evident from the presence of alunite in some samples. Areas with significant abundances of zinc sulfates, zinc sulfide and elemental sulfur were also detected. These results provide a first-time window into the complex array of inorganic species that can be present in such composite alum-treated objects.

The reaction of N,N′-bis(dicyclohexylphosphinomethyl)dihydroperimidine (H2C(NCH2PCy2)2C10H6-1,8, 1a) with [RuCl2(PPh3)3] in THF affords the perimidinylidene-based N-heterocyclic carbene (per-NHC) pincer complex [RuCl2(OC4H8){═C(NCH2PCy2)2C10H6}] (2) via chelate-assisted double C–H activation. In contrast, the reactions of the tetraphenyl analogue H2C(NCH2PPh2)2C10H6 (1b) with [RuCl2(PPh3)3] and of 1a with [RuCl(R)(CO)(PPh3)2] (R = Ph, CH═CHPh) do not result in C–H activation but rather give the asymmetric, PNP-coordinated complexes [RuCl2(PPh3){κ3P,N,P′-CH2(NCH2PPh2)2C10H6}] (3) and [RuCl(R)(CO){κ3P,N,P′-CH2(NCH2PCy2)2C10H6}] (R = Ph (4), CH═CHPh (5)), respectively, in which the ruthenium migrates rapidly between nitrogen donors. This provides insight into the mechanistic pathway by which the proligands 1 undergo per-NHC formation, as demonstrated by the thermal conversion of 4 to [RuHCl(CO){═C(NCH2PCy2)2C10H6}] (6) and benzene.

The reaction of HB(NCH2PPh2)2C6H4-1,2 with [MCl2(PPh3)3] (M = Ru, Os) affords the six-coordinate σ-borane complexes [MCl2(PPh3){σ-BH-κ2-P,P′-HB(NCH2PPh2)2-C6H4}], in which the B–H bond remains intact while coordinated to the metal center. Replacement of the unique phosphine by π-acceptor ligands, e.g., CO and CNC6H2Me3, induces B–H activation followed by spontaneous dehydrochlorination with the formation of the boryl pincer complexes [RuCl(CA)2{B(NCH2PPh2)2C6H4}] (A = O, NC6H2Me3-2,4,6).

The reactions of 1,8-diaminonaphthalene with paraformaldehyde and secondary phosphines (HPR2, R = Ph, Cy) directly afford N,N′-bis(phoshinomethyl)dihydroperimidines H2C(NCH2PR2)2C10H6 (R = Ph (1a), Cy (1b)), the methylene group of which undergoes chelate-assisted double C–H activation with [RhCl(PPh3)3] to afford dihydroperimidine-derived N-heterocyclic pincer carbene (per-NHC) complexes [RhCl{═C(NCH2PR2)2C10H6}] (R = Ph (2a), Cy (2b)). Insight into the mechanism of these C–H activation processes is provided by the reaction of 1b with [IrCl(CO)(PPh3)2] to provide the dihydroperimidinyl-hydrido complex [IrHCl(CO){CH(NCH2PR2)2C10H6}] (3b), which in turn reacts with silver salts Ag[Y] to afford, via hydride abstraction and subsequent C–H activation, the per-NHC ligated salts [IrHCl(CO){═C(NCH2PR2)2C10H6}] ([4b]Y, Y = PF6, SbF6, PO2F2).

The reaction of [Et4N][Mo(CSe)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) with [Rh2(μ-Cl)2(η4-cod)2] (cod = cyclo-octa-1,5-diene) results in the formation of the tetrametallic com...

The successive treatment of terminal alkynes, HC≡CR (R = C6H4Me-4, SiMe3), with nBuLi and gray selenium affords LiSeC≡CR, which in turn reacts with [FeCl(CO)2(η-C5H5)], [NiCl(PPh3)(η-C5H5)], and [M...

The reactions of N,N'-bis(phosphinomethyl)dihydroperimidine pro-ligands H2C(NCH2PR2)2C10H6 (R = Cy 1a, R = Ph 1b) with [RuCl2(PPh3)3] give markedly different products. Chelate-assisted double C-H activation in the former affords the perimidinylidene-based N-heterocyclic carbene (per-NHC) pincer complex [RuCl2(OC4H8){κ(3)-P,C,P'-C(NCH2PCy2)2C10H6}] (2), while the latter reaction provides the asymmetric PNP-coordinated complex [RuCl2(PPh3){κ(3)-P,N,P'-CH2(NCH2PPh2)2C10H6}] (3), in which no C-H activation has occurred. Subsequent reactions of the per-NHC complex 2 with carbon monoxide and mesityl isocyanide readily displaced the labile THF ligand to afford the complexes [RuCl2(CA){κ(3)-P,C,P'-C(NCH2PCy2)2C10H6}] (A = O 4, A = NC6H2Me35). Double C-H activation of 1a and 1b was significantly more facile on reaction with [OsCl2(PPh3)3], providing the per-NHC complexes [OsHCl(PPh3){κ(3)-P,C,P'-C(NCH2PR2)2C10H6}] (R = Cy 7a, R = Ph 7b, respectively), each as two isomers. The reactions of 1b with [Ru2(μ-Cl)2Cl2(η-C6H3Me3)2] or [AuCl(THT)] (THT = tetrahydrothiophene) provide the bimetallic complexes [Ru2{μ-H2C(NCH2PPh2)2C10H6}Cl4(η-C6H3Me3)2] (8) and [Au2{μ-H2C(NCH2PPh2)2C10H6}Cl2] (9) without C-H activation occurring.

The reaction of [Et4N][Mo(CSe)(CO)2(Tp*)}] (Tp* = hydrotris(dimethylpyrazolyl)borate) with [Ir(NCMe)(CO)(PPh3)2]BF4 results not in the anticipated isoselenocarbonyl complex [(Tp*)(CO)2Mo−CSe−Ir(CO)...