Excimer and Exciplex Formation in Gold(I) Complexes Preconditioned by Aurophilic Interactions

CITATION: Schmidbaur, H. & Raubenheimer, H. G. 2020. Excimer and Exciplex Formation in Gold(I) Complexes Preconditioned by Aurophilic Interactions. Angewandte Chemie International Education, 59(35):14748-14771. doi:10.1002/anie.201916255The original publication is available at https://onlinelibrary.wiley.com/journal/15213773Excimers and exciplexes are defined as assemblies of atoms or molecules A/A’ where interatomic/intermolecular bonding appears only in excited states such as [A2]* (for excimers) and [AA’]* (for exciplexes). Their formation has become widely known because of their role in gas-phase laser technologies, but their significance in general chemistry terms has been given little attention. Recent investigations in gold chemistry have opened up a new field of excimer and exciplex chemistry that relies largely on the preorganization of gold(I) compounds (electronic configuration AuI (5d10)) through aurophilic contacts. In the corresponding excimers, a new type of Au···Au bonding arises, with bond energies and lengths approaching those of ground-state Au@Au bonds between metal atoms in the Au0 (5d106s1) and AuII(5d9) configurations. Excimer formation gives rise to a broad range of photophysical effects, for which some of the relaxation dynamics have recently been clarified. Excimers have also been shown to play an important role in photoredox binuclear gold catalysis.https://onlinelibrary.wiley.com/doi/10.1002/anie.201916255Publishers versio

Preparation, Structure and Gold(I) Complexation of p-Xylylene-1,4-diphosphines

Dedicated to Professor Alfred Schmidpeter on the occasion of his 75 th birthday 1,4-Dimethyl-2,5-di(phosphinyl)benzene (1) was prepared in high yield in a four-step synthesis from 1,4-dibromo-2,5-dimethyl-benzene. The intermediates with (Et 2 N) 2 P and Cl 2 P groups (2, 3) with the corresponding substitution pattern have been isolated and structurally characterized. All three compounds (1 -3) adopt a centrosymmetrical conformation with one of the P-X bonds of each X 2 P group located in the ring plane while the other reaches out from this plane in a roughly perpendicular orientation. Distortions of the ring and its substituents from a standard planar hexagonal geometry are readily explained by invoking steric and inductive effects. The crystal structure of 1,4-dibromo-2,5-dimethyl-benzene has also been determined for reference purposes. Compound 1 was employed as a substrate for auration by tri(gold)oxonium salts of the type {[(R 3 P)Au] 3 O}BF 4 . Hexanuclear complex salts of the type {[(R 3 P)Au] 3 P(C 6 H 2 Me 2 )P[Au(PR 3 )] 3 }(BF 4 ) 2 were obtained in almost quantitative yield with R 3 P = t Bu 3 P (4) and Ph 3 P (5). The former (4) has the higher thermal stability, it could be crystallized and its structure determined. It features a conformation in which the xylene plane bisects one of the Au-P-Au angles at both tetrahedrally coordinated central phosphorus atoms placing its methyl groups in sterically least hindered positions. Compound 5 is labile in solution and shows rapid ligand exchange on the NMR time scale. The limited stability has also been confirmed by mass spectrometry. Similar structural details and differences in stability were observed in the related trinuclear gold complexes based on 1-naphthyl-phosphine, which were prepared as reference materials using the same preparative procedure. Of the two compounds {(1-C 10 H 7 )-P[Au(PR 3 )] 3 }BF 4 , with R 3 P = t Bu 3 P (6) and Ph 3 P (7), the former is the more stable species. In the solid state the cation approaches mirror symmetry in a conformation comparable to that of 4. Compound 7 is thermally labile and shows a rapid ligand exchange in solution

M e t hylsi lyl hyd roxylami nes: Preparative, Spectroscopic and Ab initio Studiest

Methylsilylhydroxylamines [ (MeH,Si),NOMe, (MeH,Si) MeNOMe, Me,NOSiH,Me] have been prepared from bromo(methy1)silane and the corresponding methylhydroxylamines in the presence of an auxiliary base (triethylamine or N,N,N',N'-tetramethylethylenediamine). The compounds were studied by N M R spectroscopy of all elements present ( l H , 13C, 15N, 170, 29Si). The magnitude of the one-bond coupling constants 1J('5N29Si) is interpreted in terms of the hybridization associated with the pyramidal co-ordination of nitrogen, a unique structural feature in Si/N chemistry. Ab initiu studies confirmed these structural predictions. Singly silylated hydroxylamines have been shown to be more strongly pyramidal than doubly silylated ones. Calculations on the model compound (H,Si),NOMe gave a barrier to inversion at nitrogen of 9.7 kcal mol-'. This inversion is accompanied by a partial rotation around the N-0 bond. The has a planar co-ordination at the nitrogen atom, has been maintained ever since, and during the last 40 years the structures of a large number of silylamines have been determined.2 As a general rule it was derived from these results that all compounds with doubly and triply silylated nitrogen atoms exhibit a planar geometry at n i t r~g e n .~ Only for a few monosilylated amines deviations from a planar arrangement of the nitrogen substituents occur, but with significant variations for the gas phase and the solid state. p,d, B~n d i n g ,~ formerly the most widespread hypothesis to explain this and other unique properties of silylamines, like low basicity at nitrogen and short Si-N bonds, was shown to be rather insignificant, and p,. interactions (negative hyperconjugation, anomeric effect) and an electrostatic repulsion model ' have since been introduced as more meaningful approaches. Compounds with a wide variety of substituents at the silicon part of the molecules have been structurally studied, but the variations of nitrogen substituents have been limited to silylated hydrazines some of which were presented in previous papers from this laboratory.8 For this class of Si/N compounds with nitrogen in its oxidation state -11, planarity at nitrogen induced by silyl substituents appears to be also well established.' As a continuation of these studies we have now investigated silylated hydroxylamines bearing oxygen as a very electronegative substituent at nitrogen in its oxidation state -I. In this context we recently reported the unique structure of 0-methyl-N,N-bis(ptolylsily1)hydroxylamine 1, oneofonly a few doubly N-silylated compounds with a pyramidal co-ordination sphere at nitrogen. ' ' t Non-SI unit employed: cal = 4.184 J. 1 As a follow-up to this work, and as a part of our current search for new single-source feedstock precursors for chemical vapour deposition ' (CVD) of silicon nitride and oxynitride films, ' we are now examining low-molecular-weight silylhydroxylamines with low carbon contents and high volatilities. These small molecules should also allow a direct comparison of experimental data with the results of more sophisticated theoretical calculations of structure and bonding. Results and Discussion Preparation of Methylsilylhydroxy1amines.-Since compounds with silyl groups H,Si are generally pyrophoric, methylsilyl groups, the organosilyl groups with the lowest carbon content, were chosen for this study. Bromo(methy1)silane is a powerful silylating agent for N H and OH functions and reacts with 0-methyl, N,O-dimethyl-and N,N-dimethylhydroxylamine in the presence of triethylamine to give the silylated hydroxylamines 2,3 and 4, respectively (Scheme 1). The compounds have low boiling points (97, 61 and 58 "C, respectively), and separation from the solvents and from the excess of triethylamine is difficult. These complications can be overcome by a solvent-free reaction mode and by using N,N,N',N'-tetramethylethylenediamine (tmen) as the dehydrohalogenating agent. The advantage of tmen is its dibasic nature. Since both di-and mono-protonated tmen salts are non-volatile

The experimental gas-phase structures of 1,3,5-trisilylbenzene and hexasilylbenzene and the theoretical structures of all benzenes with three or more silyl substituents

The structures of 1,3,5-trisilylbenzene and hexasilylbenzene in the gas phase have been determined by electron diffraction, and that of 1,3,5-trisilylbenzene by X-ray crystallography. The structures of three trisilylbenzene isomers, three tetrasilylbenzenes, pentasilylbenzene and hexasilylbenzene have been computed, ab initio and using Density Functional Theory, at levels up to MP2/6-31G*. The primary effect of silyl substituents is to narrow the ring angle at the substituted carbon atoms. Steric interactions between silyl groups on neighbouring carbon atoms lead first to displacement of these groups away from one another, and then to displacement out of the ring plane, with alternate groups moving to opposite sides of the ring. In the extreme example, hexasilylbenzene, the SiCCSi dihedral angle is 17.8(8)°

Gold coordination during homogeneous alkyne and allene cyclisation catalysis: Coordination to substrates, to ancillary ligands and in intermediates

The ever-increasing role of homogeneous gold catalysis in organic synthesis and the consequent need to be able to rationally control the rate and outcome of such reactions has emphasised the importance of each successive metal - carbon coordination step. Concentrating on alkyne and allene cyclisation and upon reaction mechanisms postulated on the basis of empirical and theoretical results, we have examined the coordination of gold fragments to triple bonds, the modification of gold(I) precatalysts to effect specific reaction pathways or enantioselectivity and the isolation of coordinated intermediates or model compounds thereof. Some of the recent advances that have been made in various laboratories are described in this compact review

Phenylethynyl)trimethylphosphonium Bromide and Bromoaurates(I

(Phenylethynyl)trimethylphosphonium bromide (1) has been reinvestigated by NMR spectroscopy and its crystal structure determined. In the monoclinic crystals, the cations are arranged in layers in the a-c planes, with their P-C≡C-Ph axes parallel within one layer, but alternating in consecutive layers. The bromide anions are accommodated in channels between the cations. The spectroscopic and structural results are in agreement with the special reactivity pattern documented for ethynylphosphonium salts, in particular with the sensitivity to nucleophiles which e. g. prevents standard ylide formation. A slurry of polymeric phenylethynylgold [PhC≡CAu