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A combined theoretical and experimental study on the formation and reactivity of a P-OTEMP (P-bound TEMPO (TEMPO=2,2,6,6-tetramethyl-piperidin-1-oxyl)) substituted 1,3,2-diazaphospholane W(CO)5 complex is presented, including DFT-based mechanistic details. The complex possesses a thermally labile O-N bond that cleaves homolytically yielding the transient 1,3,2-diazaphospholane-2-oxyl complex [(CO)5 W(R2 PO. )], which acts as a radical initiator for styrene polymerization under ambient conditions.

A new bis(salicylimine) ligand based on the Tröger's base scaffold was synthesized in racemic and enantiomerically pure form. Upon coordination to zinc(II) ions this ligand undergoes highly diastereoselective self-assembly into neutral dinuclear double-stranded helicates as proven by XRD analysis and via comparison of experimental ECD spectra with those simulated with quantum-chemical methods. When the racemic ligand was used, self-assembly occurs under narcissistic self-sorting resulting in the formation of a racemic pair of helicates as revealed by NMR spectroscopy and XRD analysis.

Synthesis of 1,1′-bifunctional aminophosphane complexes 3 a–e was achieved by the reaction of Li/Cl phosphinidenoid complex 2 with various primary amines (R=Me, iPr, tBu, Cy, Ph). Deprotonation of complex 3 a (R=Me) with potassium hexamethyldisilazide yielded a mixture of K/NHMe phosphinidenoid complex 4 a and potassium phosphanylamido complex 4 a′. Treatment of complex 3 c (R=tBu) and e (R=Ph) with KHMDS afforded the first examples of K/NHR phosphinidenoid complexes 4 c and e. The reaction of complex 3 c with 2 molar equivalents of KHMDS followed by PhPCl2 afforded complexes 5 c,c′, which possess a P2N-ring ligand. All complexes were characterized by NMR, IR, MS, and microanalysis, and additionally, complexes 3 b–e and 5 c′ were scrutinized by single-crystal X-ray crystallography.

One-electron oxidation of the disilicon(0) compound Si2(Idipp)2 (1, Idipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with [Fe(C5Me5)2][B(Ar(F))4] (Ar(F) = C6H3-3,5-(CF3)2) affords selectively the green radical salt [Si2(Idipp)2][B(Ar(F))4] (1-[B(Ar(F))4). Oxidation of the centrosymmetric 1 occurs reversibly at a low redox potential (E1/2 = -1.250 V vs. Fc(+)/Fc), and is accompanied by considerable structural changes as shown by single-crystal X-ray structural analysis of 1-B(Ar(F))4. These include a shortening of the Si-Si bond, a widening of the Si-Si-CNHC angles, and a lowering of the symmetry, leading to a quite different conformation of the NHC substituents at the two inequivalent Si sites in 1(+). Comparative quantum chemical calculations of 1 and 1(+) indicate that electron ejection occurs from the symmetric (n+) combination of the Si lone pairs (HOMO). EPR studies of 1-B(Ar(F))4 in frozen solution verified the inequivalency of the two Si sites observed in the solid-state, and point in agreement with the theoretical results to an almost equal distribution of the spin density over the two Si atoms, leading to quite similar (29)Si hyperfine coupling tensors in 1(+). EPR studies of 1-B(Ar(F))4 in liquid solution unraveled a topomerization with a low activation barrier that interconverts the two Si sites in 1(+).

Reactions of 3-imino-azaphosphiridine complexes 1 a,b with carbodiimides 2 a,b, isocyanates 3 a,b, and carbon dioxide are described. Whereas exchange of the carbodiimide unit occurs in the first case, an overall ring expansion takes place with phenyl isocyanate (3 a) and carbon dioxide to yield complexes 4 and 5 bearing novel 1,3,5-oxazaphospholane ligands; the isopropyl derivative 3 b did not react under these conditions. DFT calculations provide insight into the pathway of the reaction with carbon dioxide with model complex 1 c, revealing effects of initial non-covalent interactions with the substrate onto the ring bonding, thus triggering an initially masked frustrated Lewis-pair-type behavior.

A general approach to the first compounds that contain rhenium-germanium triple and double bonds is reported. Heating [ReCl(PMe3)5] (1) with the arylgermanium(II) chloride GeCl(C6H3-2,6-Trip2) (2; Trip=2,4,6-triisopropylphenyl) results in the germylidyne complex mer-[Cl2 (PMe3)3Re≡Ge-C6H3-2,6-Trip2] (4) upon PMe3 elimination. An equilibrium that is dependent on the PMe3 concentration exists between complexes 1 and 4. Removal of the volatile PMe3 shifts the equilibrium towards complex 4, whereas treatment of 4 with an excess of PMe3 gives a 1:1 mixture of 1 and the PMe3 adduct of 2, GeCl(C6H3-2,6-Trip2)(PMe3) (2-PMe3). Adduct 2-PMe3 can be selectively obtained by addition of PMe3 to chlorogermylidene 2. The NMR spectroscopic data for 2-PMe3 indicate an equilibrium between 2-PMe3 and its dissociation products, 2 and PMe3 , which is shifted far towards the adduct site at ambient temperature. NMR spectroscopic monitoring of the reaction of complex 1 with 2 and the reaction of complex 4 with PMe3 revealed the formation of two key intermediates, which were identified to be the chlorogermylidene complexes cis/trans-[Cl(PMe3)4 Re=Ge(Cl)C6H3-2,6-Trip2] (cis/trans-3) by using NMR spectroscopy. Labile chlorogermylidene complexes cis/trans-3 can be also generated from trans-[Cl(PMe3)4 Re≡Ge-C6H3-2,6-Trip2]BPh4 (9) and (nBu4N)Cl at low temperature, and decompose at ambient temperature to give a mixture of complexes 1 and 4. Complex 4 reacts with LiI to give the diiodido derivative mer-[I2(PMe3)3Re≡Ge-C6H3-2,6-Trip2] (5), which undergoes a metathetical iodide/hydride exchange with Na(BEt3H) to give the dihydrido germylidyne complex mer-[H2(PMe3)3Re≡Ge-C6H3-2,6-Trip2] (6). Carbonylation of 4 induces a chloride migration from rhenium to the germanium atom to afford the chlorogermylidene complex mer-[Cl(CO)(PMe3)3Re=Ge(Cl)C6H3-2,6-Trip2] (7). Similarly, MeNC converts complex 4 into the methylisocyanide analogue mer-[Cl(MeNC)(PMe3)3Re=Ge(Cl)C6H3-2,6-Trip2] (8). Chloride abstraction from 4 by NaBPh4 in the presence of PMe3 gives the cationic germylidyne complex trans-[Cl(PMe3)4 Re≡Ge-C6H3-2,6-Trip2]BPh4 (9). Heating complex 4 with cis-[Mo(PMe3)4(N2)2] induces a germylidyne ligand transfer from rhenium to molybdenum to afford the germylidyne complex trans-[Cl(PMe3)4Mo≡Ge-C6H3-2,6-Trip2] (10). All new compounds were fully characterized and their molecular structures studied by X-ray crystallography, which led to the first experimentally determined Re-Ge triple- and double-bond lengths.

A series of ten palladium-bis(pyridine) complexes, as well as their corresponding platinum complexes, have been synthesized. The pyridine ligands in each series carried different σ-donor and/or π-acceptor/donor substituents at the para-position of their pyridine rings. These complexes were analysed by NMR spectroscopy, X-ray crystallography, (tandem) MS, and isothermal titration calorimetry (ITC) to validate whether these methods allowed us to obtain a concise and systematic picture of the relative and absolute thermodynamic stabilities of the complexes, as determined by the electronic effects of the substituents. Interestingly, the NMR spectroscopic data hardly correlated with the expected substituent effects but the heteronuclear platinum-phosphorus coupling constants did. Crystallographic data were found to be blurred by packing effects. Instead, tandem MS and ITC data were in line with each other and followed the expected trends.

When 2,4-dimethylphenol is anodically treated, a dehydrotetramer with four contiguous stereocentres is readily obtained on a multi-gram scale. The substitution of a 2,4-dimethyl-phenoxy fragment by several amines was demonstrated, and the best results were obtained with primary amines. Optically pure α-chiral aliphatic amines yield diastereomeric mixtures that can be separated in most cases. The basic amine causes a partial hemiketal-opening of the bisbenzofuran moiety leading to an equilibrium within an α,β-unsaturated cyclohexenone. This dynamic behaviour occurs on the time scale of NMR spectroscopy and is also found by X-ray analysis providing a consistent picture.

An efficient method for the synthesis of the first N-heterocyclic carbene (NHC)-stabilized halosilylidyne complexes is reported that starts from SiBr(4). In the first step, SiBr(4) was treated with one equivalent of the N-heterocyclic carbene 1,3-bis[2,6-bis(isopropyl)phenyl]imidazolidin-2-ylidene (SIdipp) to give the 4,5-dihydroimidazolium salt [SiBr(3)(SIdipp)]Br (1-Br), which then was reduced with potassium graphite to afford the silicon(II) dibromide-NHC adduct SiBr(2)(SIdipp)(2-Br) in good yields. Heating 2-Br with Li[CpCr(CO)(3)] afforded the complex [Cp(CO)(2)Cr=SiBr(SIdipp)] (3-Br) upon elimination of CO. Complex 3-Br features a trigonal-planar-coordinated silicon center and a very short CrSi double bond. Similarly, the reaction of SiCl(2)(SIdipp) (2-Cl) with Li[CpCr(CO)(3)] gave the analogous chloro derivative [Cp(CO)(2)Cr=SiCl(SIdipp)] (3-Cl). Complex 3-Br undergoes an NHC exchange with 1,3-dihydro-4,5-dimethyl-1,3-bis(isopropyl)-2H-imidazol-2-ylidene (IMe(2)iPr(2)) to give the complex [Cp(CO)(2)CrSiBr(IMe(2)iPr(2))(2)] (4-Br). Compound 4-Br features a distorted-tetrahedral four-coordinate silicon center. Bromide abstraction occurs readily from 4-Br with Li[B(C(6)F(5))(4)] to give the putative silylidene complex salt [Cp(CO)(2)Cr=Si(IMe(2)iPr(2))(2)][B(C(6)F(5))(4)], which irreversibly dimerizes by means of an Si-promoted electrophilic activation of one carbonyl oxygen atom to yield the dinuclear siloxycarbyne complex [Cp(CO)Cr{(μ-CO)Si(IMe(2)iPr(2))(2)}(2-)Cr(CO)Cp][B(C(6)F(5))(4)](2) (5). All compounds were fully characterized, and the molecular structures of 2-Br-5-Br were determined by single-crystal X-ray diffraction. DFT calculations of 3-Br and 3-Cl and their carbene dissociation products [Cp(CO)(2)Cr=Si-X] (X=Cl, Br) were carried out, and the electronic structures of 3-Br, 3-Cl and [Cp(CO)(2)Cr=Si-X] were analyzed by the natural bond orbital method in combination with natural resonance theory.

Five racemic dissymmetric bis(pyridyl) ligands based on 2,8- or 3,9-difunctionalised Tröger's base derivatives have been synthesised. Only those derived from a 2,8-difunctionalised scaffold were found to undergo selective self-assembly to discrete self-assembled dinuclear metallosupramolecular aggregates of rhomboid shape upon coordination to cis-protected Pd(2+) or Pt(2+) ions, as evidenced by ESI mass spectrometry, NMR spectroscopy and single-crystal X-ray diffraction. Interestingly, these processes were found to be highly diastereoselective leading to the formation of C(2v)-symmetric heterochiral assemblies in a self-discriminating manner.

Two racemic derivatives of Tröger's base, the 2,8-diboronic acid ester 6 and the 3,9-dibromo-substituted derivative 5, were synthesized and successfully resolved by HPLC on a chiral stationary Whelk-01 phase on a semipreparative scale, thereby giving rise to both enantiomers in a pure form. These functionalized C(2)-symmetric building blocks are valuable precursors for a variety of further applications. Their absolute configurations were determined by comparison of their quantum chemically calculated CD and UV/Vis spectra with the experimental ones and were independently confirmed by X-ray diffraction analysis.