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The B-B bond activation of the diborane(4) derivatives B 2 cat 2 with the copper(I) alkoxido complex [(SIDipp)Cu-O tBu] delivers, depending on the solvent, either the linear boryl complex [(SIDipp)Cu-Bcat] from PhMe or the μ-boryl complex [((SIDipp)Cu) 2 Bcat][cat 2 B] from THF. The relevant conversion of the linear boryl complex to the μ-boryl complex occurs in the polar solvent via formal boryl anion abstraction by the Lewis acid catB-O tBu, concomitantly formed during the B-B activation. With Lewis acids such as BPh 3 or [CPh 3 ][BArF] (reversible), boryl abstraction from the linear complexes [(SIDipp)Cu-Bcat] or [(SIDipp)Cu-Bdmab] occurs and results in the μ-boryl complexes [((SIDipp)Cu) 2 Bcat/dmab][Ph 3 B-Bcat/dmab] and [((SIDipp)Cu) 2 Bcat][BArF]. The formation of [((SIDipp)Cu) 2 Bcat][cat 2 B] is generally accompanied by the concomitant formation of the μ-hydrido complex [((SIDipp)Cu) 2 H][cat 2 B]. The spiroborate [cat 2 B] - is formed from the initially formed Lewis acid/base adduct [catB-B(O tBu)cat] - presumably in a process that involves the glass surface of the reaction vessel. All complexes are thoroughly characterized structurally as well as spectroscopically, in particular with respect to the dynamic behavior of the μ-boryl complexes in solution.

Cu I -catalyzed silylation reactions involving silylboranes (in particular, pinB-SiMe 2 Ph (1)) as silyl sources have recently gained considerable attention. One of the most efficient and versatile and yet simplest catalyst systems consists of CuCN/NaOMe; however, nothing is known about the catalytically relevant species. Using an NHC-based model catalyst, copper silyl complexes of the type [(NHC)Cu-SiMe 2 Ph] have been established to be crucial species in these catalytic processes. The well-defined and spectroscopically and structurally characterized complex [(18-C-6)K][NC-Cu-OtBu] (2), as a model for the catalytic system, CuCN/NaOMe, shows comparable catalytic activity toward established, exemplary substrates (aldehydes, imines, α,β-unsaturated carbonyls) and in extension allows the efficient silylation of ketones. In addition, a number of peculiarities of the catalytic reaction are readily rationalized on the basis of the mechanistic insight already established using [(NHC)Cu-SiMe 2 Ph] as a model catalyst. Analogously to the NHC model system, the reaction of 2 with the silylborane 1 furnishes the silylcyanocuprate [(18-C-6)K][NC-Cu-SiMe 2 Ph] (3) as a potential crucial intermediate in these silylation reactions also suggesting mechanistic similarities between (NHC)Cu- and CuCN/NaOMe-based catalyst systems. Moreover, 3 and [(NHC)Cu-SiMe 2 Ph] complexes also share structurally distinctive features. In the solid state 3 either exists as a linear, two-coordinated copper complex or, depending on the conditions of crystallization, forms binuclear μ-silyl bridged dimers exhibiting very short Cu···Cu distances. Both structural motifs are also known for [(NHC)Cu-SiR 3 ] complexes. These findings give an initial insight into the versatile structural chemistry of certain silylcyanocuprates; in particular, the finding of dinuclear silylcuprates gives rise to the question whether these dimeric species are of mechanistic relevance for the catalytic processes. However, all peculiarities of the investigated catalytic reaction can readily be rationalized on the basis of the mechanistic details established using (NHC)Cu model complexes.

A series of complexes of the type [(NHC)Cu-ER3] (NHC = IDipp, IMes, ItBu, Me2IMe, and ER3 = SiMe2Ph, SiPh3, SnMe3) and [(NHC)Cu-R'] (NHC = IDipp, Me2IMe and R' = Ph, C≡CPh) was synthesized in good yields by the reaction of the corresponding [(NHC)Cu-OtBu] complex with the respective silylborane pinB-ER3 (pin = OCMe2CMe2O; ER3 = SiMe2Ph, SiPh3), the stannylborane ((C2H4)(iPrN)2)B-SnMe3, or a boronic acid ester pinB-R' (R' = Ph, C≡CPh). Solid structures of all complexes were systematically studied by X-ray diffraction analysis. The solid state structures of the complexes [(NHC)Cu-ER3] show a dependence of the structural motif from the steric properties of the NHC ligand. The sterically demanding NHC ligands (IDipp, IMes, ItBu) lead to monomeric, linear complexes [(NHC)Cu-ER3], while with the less demanding Me2IMe ligand, polynuclear, μ-ER3-bridged complexes with ultrashort Cu···Cu distances are observed. For the related complexes [(NHC)Cu-R'] no analogous complexes with bridging anionic ligands are realized. Instead, irrespective of the NHC ligand, linear coordinated copper complexes of different types are formed. (29)Si heteronuclear solution NMR spectroscopic data on [(NHC)Cu(I)-SiR3] exhibit distinctly different chemical shifts for the (in the solid state) monomeric and dimeric complexes suggesting different structure types also in solution. This agrees well with the observation of a trinuclear complex [(Me2IMe)Cu-SnMe3]3 both in the solid state and in solution. Initial catalytic studies suggest that [(NHC)Cu-OtBu] complexes (NHC = ItBu, Me2IMe) are, in addition to the established [(IDipp)Cu-OtBu] complex, efficient precatalysts for the silylation of aldehydes and α,β-unsaturated ketones with pinB-SiMe2Ph.

A series of trimethylstannyl potassium complexes [K(L)SnMe3] with different auxiliary ligands L (L = 18-C-6, (TMEDA)2 (TMEDA = tetramethylethylenediamine), and (12-C-4)2) were synthesized by alkoxide-induced B-Sn bond cleavage. X-ray structure determinations were performed for all these complexes, and the structural chemistry was studied in detail. For L = 18-C-6 and (TMEDA)2 the solid state structures comprise polymeric [K(L)SnMe3]n chains containing bidentate trimethylstannyl anions bridging two [K(L)](+) ions, featuring unsymmetrical coordination of the [K(L)](+) ion by K-Sn and K-H3C interactions as a central structural motif. In contrast, for L = (12-C-4)2, separated [K(12-C-4)2](+) and [SnMe3](-) ions are observed. Unexpectedly, in the presence of tetrahydrofuran (THF), [K(18-C-6)SnMe3]n forms upon crystallization a new species consisting of separated [K(18-C-6)(THF)2](+) and [(Me2SnCH3)K(18-C-6)SnMe3](-) ions. In this unsymmetrical anion two trimethylstannyl anions coordinate a single [K(18-C-6)](+) ion; one trimethylstannyl anion coordinates via a K-Sn interaction, and the second coordinates via a K-H3C interaction. Simulations of the mechanochemical properties (compliance constants) applying approximated density functional theory revealed that both interactions are very soft and are of comparable strength. Moreover, according to our gas phase simulations the unsymmetrically coordinated [(Me2SnCH3)K(18-C-6)SnMe3](-) is indeed thermodynamically favored over both possible symmetrical isomers with either K-Sn or K-H3C coordination. Furthermore, the existence of multiple species due to the two coordination modes and aggregates of [K(18-C-6)SnMe3] in solution is suggested by NMR spectroscopic studies using (1)H, NOESY/ROESY, and (1)H pulsed field gradient diffusion experiments.

Unsymmetrical 1-(arylimino)-3-(2-hetarylimino)isoindolines have been prepared from 1,3-diiminoisoindoline, an arylamine (aniline, 2-methylaniline, 2-iodoaniline), and a heteroaromatic amine (2-amino-6-methylpyridine, 2-amino-4-methylthiazole) in a stepwise manner by two consecutive condensations. The metalation reactions of these compounds with palladium(II) acetate proceed upon cyclopalladation of the carbocyclic aryl moieties and yield unsymmetrical C, N, N pincer complexes in all cases. X-ray crystallographic analysis were performed on single crystals of hydrogen{acetato[1-phenylimino-3-(6-methylpyridylimino)isoindolinato]palladate(II)} H[(phpi)Pd(OAc)] and pyridine[1-(2-tolylimino)-3-(4-methylthiazolylimino)isoindolinato]palladium(II) [(2-tolti)Pd(py)] by which the coordination mode, the conformation, the protonation site, and the trans influence of the carbon donor were established. For one more C, N, N pincer complex, hydrogen{acetato[1-(2-iodophenylimino)-3-(6-methylpyridylimino)isoindolinato]palladate(II)} H[(2-Iphpi)Pd(OAc)], a similar mononuclear coordination mode was confirmed by (1)H NMR spectroscopy, whereas for the product of an oxidative addition reaction of a palladium(0) precursor to the iodoaryl derivative a product with exo coordination was found. First experiments showed the effectivity of one of these complexes as a precatalyst in CC coupling reactions (Heck and Stille coupling).