The effects of isoelectronic replacement of a neutral nitrogen donor atom by an anionic carbon atom in terpyridine ruthenium(II) complexes on the electronic and photophysical properties of the resulting N,C,N'- and C,N,N'-cyclometalated aryl ruthenium(II) complexes were investigated. To this end, a series of complexes was prepared either with ligands containing exclusively nitrogen donor atoms, that is, [Ru(R(1)-tpy)(R(2)-tpy)](2+) (R(1), R(2) = H, CO(2)Et), or bearing either one N,C,N'- or C,N,N'-cyclometalated ligand and one tpy ligand, that is, [Ru(R(1)-N(/\)C(/\)N)(R(2)-tpy)](+) and [Ru(R(1)-C(/\)N(/\)N)(R(2)-tpy)](+), respectively. Single-crystal X-ray structure determinations showed that cyclometalation does not significantly alter the overall geometry of the complexes but does change the bond lengths around the ruthenium(II) center, especially the nitrogen-to-ruthenium bond length trans to the carbanion. Substitution of either of the ligands with electron-withdrawing ester functionalities fine-tuned the electronic properties and resulted in the presence of an IR probe. Using trends obtained from redox potentials, emission energies, IR spectroelectrochemical responses, and the character of the lowest unoccupied molecular orbitals from DFT studies, it is shown that the first reduction process and luminescence are associated with the ester-substituted C,N,N'-cyclometalated ligand in [Ru(EtO(2)C-C(/\)N(/\)N)(tpy)](+). Cyclometalation in an N,C,N'-bonding motif changed the energetic order of the ruthenium d(zx), d(yz), and d(xy) orbitals. The red-shifted absorption in the N,C,N'-cyclometalated complexes is assigned to MLCT transitions to the tpy ligand. The red shift observed upon introduction of the ester moiety is associated with an increase in intensity of low-energy transitions, rather than a red shift of the main transition. Cyclometalation in the C,N,N'-binding motif also red-shifts the absorption, but the corresponding transition is associated with both ligand types. Luminescence of the cyclometalated complexes is relatively independent of the mode of cyclometalation, obeying the energy gap law within each individual series.

ZnII–salphen complexes are readily accessible and interesting supramolecular building blocks with a large structural diversity. Higher‐order supramolecular assemblies, such as molecular boxes based on a bis‐ZnII–salphen building block and various ditopic bipyridine ligands, have been constructed by means of supramolecular, coordinative ZnII–Npyr interactions. The use of bipyridine ligands of differing sizes enables the construction of structures with predefined box diameters. The features of the 2:2 box assemblies were investigated in detail by (variable temperature) NMR spectroscopy, UV‐visible spectroscopy, NMR titrations, and X‐ray crystallographic studies. The spectroscopic studies reveal a high association constant for the ZnII–salphen–pyridyl motif, which lies in the range 105–106 M−1. The strong interaction between the ZnII center and pyridine donors was supported by PM3 calculations that showed a relatively high Lewis acid character of the metal center in the salphen complex. Titration curves monitored by UV‐visible show a cooperative effect between the two bipyridine ligands upon complexation to the bis‐ZnII template, suggesting the formation of 2:2 complexes. The crystal structures of two supramolecular boxes have been determined. In both examples such a 2:2 assembly is present in the solid state, and the box size is different because they consist of different building blocks. Interestingly, the box assemblies line up in the solid state to form porous channels that are potentially useful in a number of applications.

Subjecting ferrocene, ruthenocene, or osmocene to the synergic amide base sodium-magnesium tris(diisopropylamido) affords a unique homologous series of metallocene derivatives of general formula [(M(C(5)H(3))(2))Na(4)Mg(4)(i-Pr(2)N)(8)] (where M = Fe (1), Ru (2), or Os (3)). X-ray crystallographic studies of 1-3 reveal a common molecular "inverse crown" structure comprising a 16-membered [(NaNMgN)(4)](4+) "host" ring and a metallocenetetraide [M(C(5)H(3))(2)](4-) "guest" core, the cleaved protons of which are lost selectively from the 1, 1', 3, and 3'-positions. Variable-temperature NMR spectroscopic studies indicate that 1, 2, and 3 each exist as two distinct interconverting conformers in arene solution, the rates of exchange of which have been calculated using coalescence and EXSY NMR measurements.

Summary: The isomerization of the branched 2M3BN to the linear 3PN by a DPEphosNi species has been investigated by means of variable-temperature NMR spectroscopy, and activation parameters have been determined. An intermediate in this reaction, which is formed via C-C bond activation, could be trapped by addition of ZnCl 2 , and the molecular structure of the corresponding Ni(II) complex has been determined by X-ray crystallography.Among C-C bond formation reactions, the hydrocyanation of alkenes is an attractive, yet challenging, route for the functionalization of carbon-carbon double bonds. 1,2 The isomerization of 2-methyl-3-butenenitrile (2M3BN) to 3-pentenenitrile (3PN), for example, is closely related to hydrocyanation and is at the same time an important step in the industrial adiponitrile process. 3 In combination with Ni(cod) 2 , all classes of bidentate phosphorus ligands (phosphines, 4,5 phosphinites, 6 phosphonites, 4,7 and phosphites 8 ) catalyze the isomerization, without the addition of Lewis acids. However, the influence of ligand parameters on this conversion still remains unknown. The isomerization is, in fact, a suitable reaction to study reductive elimination to the final product 3PN without the deactivation of the catalyst usually caused by HCN during hydrocyanations. 9,10 We started a spectroscopic investigation of the isomerization of 2M3BN to 3PN catalyzed by DPEphos/ Ni(cod) 2 to study the reductive elimination of nitriles, which is the crucial step in catalytic hydrocyanation reactions. In fact, we were moved to report on our results because of recent contributions in this field by Santini et al. 11 and Chaudret et al. 5 Upon addition of 1 equiv of DPEphos to Ni(cod) 2 in toluene-d 8 the 31 P NMR spectrum displays a singlet at δ 33.1 ppm for the species (DPEphos)Ni 0 (cod) (1) (Scheme 1). This signal disappears on addition of approximately 3 equiv of 2M3BN at -35°C, and two doublets appear at δ 21.3 and 24.2 ppm, with 2 J PP ) 38 Hz. These resonances correspond to (DPEphos)Ni 0 -(2M3BN) (2), with 2M3BN coordinating most likely through its alkene bond; the η 2 -alkene complex (DPEphos)Ni 0 (styrene) gives a very similar 31 P NMR spectrum, which shows two doublets at δ 20.2 and 22.9 ppm with 2 J PP ) 44 Hz. When the temperature is raised to +25°C, the two doublets of 2 disappear and a signal could no longer be detected in the 31 P NMR spectrum.The 1 H NMR spectrum shows broad signals at δ 4.5 (CHCH 2 ), 3.4 (CHCH 3 ), 2.4 (1H, CH syn H anti ), 1.6 (CH 3 ), and 1.2 (1H, CH syn H anti ) ppm. Increasing the temperature to +35°C causes slow isomerization of 2M3BN to 3PN, indicated by the methyl signals in the 1 H NMR spectrum. The 3PN analogue (DPEphos)Ni 0 (3PN) (5) could not be detected with VT NMR spectroscopy when approximately 5 equiv of 3PN was added to 1. However, 1 disappears and the same broad signals in the 1 H NMR spectrum occur which were detected upon warming of 2. We ascribe this spectrum to (DPEphos)Ni II (C 4 H 7 )(CN) (3), which is formed by oxidative addition of 2M3BN or

The formation of a dimeric structure of a nonsymmetric Zn(II)salphen complex is reported. The X-ray molecular structure show the formation of an oxygen-bridged species (2). In addition to this structure, a pyridine-ligated complex and an 1:2 dabco/Zn(II)salphen supramolecular assembly (dabco = diazabicyclo[2.2.2]octane) are presented. Their coordination behavior has been studied and can be correlated with the substitution pattern of the salphen ligand and the donor-strength of the involved axial ligands. The Zn(II)salphen building blocks bind in a cooperative fashion to the dabco template, the second unit being bound 4 times more strongly.