Michael C. Jennings

Self-assembly of rings, catenanes, and a doubly braided catenane containing gold(I): the hinge-group effect in diacetylide ligands.

Reaction of the flexible dialkynyldigold(I) precursors X(4-C6H4OCH2C-CAu)2 with 1,4-bis(diphenylphosphino)butane gave complexes of formula [[[mu-X(4-C6H4OCH2CCAu)2[mu-(Ph2PCH2CH2CH2CH2PPh2)]]n]. The complexes exist as 25-membered ring compounds with n = 1 when X = O or S, as [2]catenanes with n = 2 when X = CH2 or CMe2, and as a unique doubly braided [2]catenane, containing interlocked 50-membered rings with n = 4 when X = cyclohexylidene. These compounds form easily and selectively by self-assembly; reasons for the selectivity are also discussed.

Fine-tuning the single-molecule magnet properties of a [Dy(III)-radical]2 pair.

A supramolecular species composed of a pair of nonequivalent Dy(III)-radical complexes exhibits single-molecule magnet (SMM) properties. The weak effective antiferromagnetic coupling between the Dy(III) ions can be compensated by application of a small (700 Oe) dc field, revealing the relaxation mode of the two distinct SMMs. These unique results illustrate how the dynamics of a supramolecular [Dy-Radical]2 SMM can be fine-tuned by the exchange-bias and an applied magnetic field.

Controlled Self-Assembly of Cyclic Gold(I) Complexes: The First Family of Organometallic Catenanes

The value of n in Ph(2)P(CH(2))(n)PPh(2) controls whether a simple ring or a [2]catenane is formed in the reaction with a digold(I) diacetylide. Simple macrocyclic gold complexes are obtained for n=2 and the family of organometallic [2]catenanes for n=4 and 5 (see structure); a mixture of these products as well as a third isomer results when n=3.

Tuning of Electrogenerated Silole Chemiluminescence

Increasing interest in p-conjugated compounds containing silole rings (1-silacyclopentadiene) is to a large extent due to recent exploitation for applications such as electrochemiluminescent sensors and light-emitting diodes. Their unique photophysical and electronic properties arise from the particularly low lying LUMO owing to s*–p* conjugation between the s* orbital of two exocyclic s bonds on the silicon atom and the p* orbital of the butadiene moiety. We recently reported the synthesis of donor–acceptor siloles and oligomeric ethynyl siloles, and the electrogenerated chemiluminescence (ECL) of several silole-based chromophores. We also reported a series of 2,5-bis(arylethynyl) siloles in which a curious improvement of photoluminescence (PL) quantum efficiency from 9 to 63% was achieved by increasing the steric bulk on the silicon atom and 2,5substituents. It seemed plausible that the enhanced luminescence resulting from the highly improved quantum efficiency was due to increasing the energy barriers for nonemissive decay processes. However, these electronic improvements did not translate to ECL, and the efficiencies of some ethyleneand ethynyl-substituted siloles were only in the range of 0.001 to 0.1 relative to 9,10-diphenylanthracene (DPA), owing to the instability of their radical cations needed for ECL generation. Herein we report that successful tuning of the electrochemical potentials and of silole–thiophene hybrid chromophores results in higher stability of the radical cations and ultimately in improved ECL efficiency. Considering that 1,1-dimethyl-2,5-bis(2-thienyl)-3,4diphenylsilole (3a) and 1,1-dimethyl-2,5-bis[(2,2’-bithiophen)-5-yl]-3,4-diphenylsilole (4a) are efficient electrontransporting materials, we expected that replacement of the methyl substituents with larger isopropyl, tert-butyl and nhexyl groups would augment the energy barriers for nonemissive decay processes, stabilize the radical cations generated electrochemically, and thus result in enhanced photoluminescence and ECL. Therefore the target chromophores, 3b–d and 4b–d, were prepared as shown in Scheme 1. Intramolecular cyclization of bis(phenylethynyl) dialkyl

Synthesis and magnetic properties of a 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl dimanganese complex.

A spin-bearing bis-bidentate ligand, designed from a pyrimidyl-substituted R-CN2S2 neutral radical, is used to co-ordinate two Mn(II) metal centres yielding a thermally stable complex with antiferromagnetic coupling between the ligand-centred spin and the metal-centred spins, and thus an overall ferrimagnetic coupling scheme with a ground state S = 9/2.

Novel rhodathiaborane complexes derived from [(PPh3)2RhSB9H10]

The compound [8,8-(PPh3)2-8,7-RhSB9H10], (1), has a formal closo electron count but a nido structure, exhibits unusual fluxional behaviour in solution and reacts to give both closo and nido compounds, e.g., closo-[2,3-(PPh3)2-3-(Cl)-µ-2; 3-(Cl)-2-(Ph2P[graphic omitted]H8], (2), and nido-[8,8-(PPh3)2-µ-8;9-(S2CH)-8,7-RhSB9H9], (3); the structures of (1), (2), and (3) were determined by X-ray crystallographic methods.

An imidazol-2-ylidene borane complex exhibiting inter-molecular [C–Hδ+⋯Hδ−–B] dihydrogen bonds

The structure of 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene·BH3, (1·BH3) has been determined by X-ray crystallography; the high melting solid exhibits head-to-tail alignment of the molecular dipoles in the solid state, with the closest intermolecular contact being a simple well-defined example of an unconventional [C–Hδ+⋯Hδ−–B] dihydrogen bond.

Macrocyclic gold(I) complexes and [2]catenanes containing carbonyl functionalized diacetylide ligands

Abstract The carbonyl derivatized bis(alkyne) OC(4-C 6 H 4 OCH 2 CCH) 2 was converted into the imine derivatives RNC(4-C 6 H 4 OCH 2 CCH) 2 [R=OH, NHC(O)NH 2 , NHC 6 H 3 -2,4-(NO 2 ) 2 ] and into the 4-bromomethyl-1,3-dioxolane derivative BrCH 2 C 2 H 3 O 2 C(4-C 6 H 4 OCH 2 CCH) 2 . The alkyne units in these compounds react with [AuCl(SMe 2 )] in the presence of base to form the corresponding digold(I) diacetylide complexes, that exist as insoluble oligomers or polymers. They reacted with the diphosphines Ph 2 PZPPh 2 [Z=CC, trans -HCCH and (CH 2 ) n , n =3–5] to give macrocyclic gold(I) complexes of the type [Au 2 (μ-LL)(μ-PP)], where LL is the diacetylide and PP the diphosphine ligand. The ability of these macrocyclic complexes to self-assemble to [2]catenanes has been studied. The ketone and imine derivatives do not form [2]catenanes because the orientation of the aryl groups is unfavorable, but the 1,3-dioxolane derivatives may catenate if the ring size is optimum.

Dicationic Sulfur Analogues of N‐Heterocyclic Silylenes and Phosphenium Cations

DABling with sulfur: Sulfur(II) dications can be prepared using alpha-diimines to stabilize the positive charge (see scheme; DAB = diazabutadiene, Dipp = 2,6-diisopropylphenyl, OTf = CF(3)SO(3)). The bonding is best described as that of a N,N-chelated sulfur(II) dication; these species represent the first sulfur-based structural mimics of N-heterocyclic silylene compounds and phosphenium cations.

The direct reaction of the tBu-DAB ligand with SeCl4: a redox route to selenium–nitrogen heterocycles

The reaction of SeCl4 with the ubiquitous tert-butyl-substituted diazabutadiene ligand results in the isolation of a rare example of a 1,2,5-selenadiazolium cation, representing a novel route to Se-N ring formation; these heterocycles can be derivatised at selenium, which has led to the identification of a short Se...N secondary bonding interaction.