Novel gold(I) "click" carbene(1,2,3-triazolylidene) complexes have been synthesised, characterised and exploited for the self-assembly of a metallomacrocycle and as precatalysts for gold(I)-catalysed reactions.

The [Ni(IMes)2]-catalyzed transformation of fluoroarenes into arylboronic acid pinacol esters via C-F bond activation and transmetalation with bis(pinacolato)diboron (B2pin2) is reported. Various partially fluorinated arenes with different degrees of fluorination were converted into their corresponding boronate esters.

N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) are of great interest, as their electronic and steric properties provide a unique class of ligands and organocatalysts. Herein, substitution reactions involving novel carbonyl complexes of rhodium and nickel were studied to provide a deeper understanding of the fundamental electronic factors characterizing CAAC(methyl) , which were compared with the large array of data available for NHC and sterically more demanding CAAC ligands.

The first synthesis of cyclic (alkyl)(amino)carbenes (cAACs) was reported in 2005, and since then this class of carbenes has been on a victory tour in main-group-element and transition-metal chemistry. CAACs are easy to synthesize and among the most nucleophilic (σ-donating) and simultaneously most electrophilic (π-accepting) carbenes known to date. These properties have led to a vast number of applications of cAACs in main-group-element chemistry in, for example, the activation of small-molecule compounds and enthalpically strong bonds, as well as in the stabilization of highly reactive main-group- [a] .Udo's major research interests lie in the fields of main-group-element and transition-metal chemistry with an emphasis on the chemistry of NHCs and related species in inorganic chemistry, the catalytic activation of small-molecule compounds and the manipulation of fluorinated organic molecules in the coordination sphere of transition metals.

We report the isolation and detailed structural characterization, by solid-state and solution NMR spectroscopy, of the neutral mono- and bis-NHC adducts of bis(catecholato)diboron (B2 cat2 ). The bis-NHC adduct undergoes thermally induced rearrangement, forming a six-membered -B-C=N-C=C-N-heterocyclic ring via C-N bond cleavage and ring expansion of the NHC, whereas the mono-NHC adduct is stable. Bis(neopentylglycolato)diboron (B2 neop2 ) is much more reactive than B2 cat2 giving a ring expanded product at room temperature, demonstrating that ring expansion of NHCs can be a very facile process with significant implications for their use in catalysis.

C-F and C-H bond activation reactions of polyfluoroaromatics at the cyclic (alkyl)(amino)carbene (cAAC) cAAC (1) are reported. Studies on the C-F bond activation using the cAAC-stabilized nickel(0) complex [Ni(cAAC ) ] (2) have shown that 2 does not react with fluorinated arenes. However, these investigations led to the observation of C-F bond cleavage of perfluorinated arenes by the carbene ligand cAAC (1) itself. The reaction of 1 with C F , C F -C F , C F -CF , and C F N afforded the insertion products of cAAC into one of the C-F bonds of the substrate, that is, the C-F bond activation products (cAAC )F(Ar ) (Ar =C F 4 a, C F -C F 4 b, C F -CF 4 c, C F N 4 d). These products decompose readily upon heating to 80 °C within a few hours in solution with formation of ionic iminium salts [(cAAC )(Ar )][X] 6 a-d or neutral alkenyl perfluoroaryl imine compounds 7 a-d. The compounds (cAAC )F(Ar ) 4 a-d readily transfer fluoride, which has been exemplified by the fluoride transfer of all compounds using BF etherate as fluoride acceptor. Fluoride transfer has also been achieved starting from (cAAC )F(C F -CF ) (4 c) or (cAAC )F(C F N) (4 d) to other selected substrates such as trimethylchlorosilane, benzoyl chloride and tosyl chloride. Instead of C-F bond activation, insertion of the cAAC into the C-H bond was observed if 1 was treated with the partially fluorinated arenes C F H, 1,2,4,5-C F H , 1,3,5-C F H , and 1,3-C F H . The compounds (cAAC )H(Ar ) (Ar =C F 12 e, 2,3,5,6-C F H 12 f, 2,4,6-C F H 12 g and 2,6-C F H 12 h) have been isolated in good yields and have been characterized including X-ray analysis. Fluorobenzene C FH (pK ≈37), the least C-H acidic fluoroarene used in this study, does not react. In order to investigate the scope and limitations of this type of cAAC C-H bond activation reaction, cAAC (1) was treated with several other reagents of different C-H acidity such as imidazolium salts, imidazoles, esters, and trimethylphosphine. These investigations led to the isolation and characterization of the compounds [(cAAC )H(R Im )]X (13 a,b), (cAAC )H(Im ) (14 a-c), (cAAC )H(CH(COOCH ) ) (15 b) and (cAAC )H(CH -PMe ) (16). Deprotonation of [(cAAC )H(Me Im )][BF ] (13 a) at the cAAC carbon atom using KHMDS as a base led to isolation and structural characterization of the cAAC -NHC heterodimer (17).

In this detailed study we report on the structures of the widely employed diboron(4) compounds bis(pinacolato)diboron (Bpin) and bis(neopentyl glycolato)diboron (Bneop), as well as bis(ethylene glycolato)diboron (Beg) and tetrakis(dimethylamino)diboron (B(NMe)), and their reactivity, along with that of bis(catecholato)diboron (Bcat) with backbone saturated and backbone unsaturared N-heterocyclic carbenes (NHCs) of different steric demand. Depending on the nature of the diboron(4) compound and the NHC used, Lewis-acid/Lewis-base adducts or NHC ring-expansion products stemming from B-B and C-N bond activation have been observed. The corresponding NHC adducts and NHC ring-expanded products were isolated and characterised via solid-state and solution NMR spectroscopy and X-ray diffraction. In general, we observed B-B bond and C-N bond activation at low temperature for Beg, at room temperature for Bneop and at higher temperature for Bcat. The reactivity strongly depends on steric effects of the NHCs and the diboron(4) compounds, as well as on the corresponding Lewis-basicity and Lewis-acidity. Our results provide profound insight into the chemistry of these diboron(4) reagents with the nowadays ubiquitous NHCs, the stability of the corresponding NHC adducts and on B-B bond activation using Lewis-bases in general. We demonstrate that B-B bond activation may be triggered even at temperatures as low as -40 °C to -30 °C without any metal species involved. For example, the reactions of Beg with sterically less demanding NHCs such as MeIm and iPrIm in solution led to the corresponding ring-expanded products at low temperatures. Furthermore, boronium [LB(OR)] and borenium [LB(OR)] cations have been observed from the reaction of the bis-borate Beg with the NHCs iPrIm and MeIm, which led to the conclusion that the activation of bis-borates with NHCs (or Lewis-bases in general) might be a facile and simple route to access such species.

The thermal dehydrogenative coupling of aryl phosphine-borane adducts with iridium complexes bearing a bis(phosphinite) pincer ligand is reported. This catalysis produces high molecular weight poly(phosphinoboranes) [ArPH-BH2]n (Ar = Ph, (p)Tol, Mes). Furthermore, we investigated the reactivity of these pincer complexes towards primary phosphines and their respective borane adducts on a stoichiometric scale.