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A comparison of the ligand substitution behavior of [ReBr(sub3)(CO)(sub3)](NEt(sub4)(sub2) and [ReBr(sub3)(CO)(sub2)(NO)NEt(sub4) in aqueous media is done. The products of the substitution reactions are isolated and characterized by means of IR, NMR, MS, and X-ray structure analysis.

The reaction of 1 equiv of the disilenide [Tip.sub.2]Si[double bond]Si(Tip)Li (Tip = 2,4,6-[super i][Pr.sub.3][C.sub.6][H.sub.2]) with para-substituted phenyl iodides, 4-X-PhI, has transferred the [Tip.sub.2]Si[double bond]Si(Tip) moiety with elimination of lithium iodide to produce the laterally functionalized disilenes [Tip.sub.2]Si[double bond]Si(Tip)(4-X-Ph) [X = H, F, Cl, Br, I). The UV-vis absorptions of the functionalized disilenes have shown a linear correlation with electronic Hammett parameters.

The synthesis of [Si.sub.5][Mes.sub.6] (Mes = 2,4,6-trimethylphenyl) consisting of an archetypal [1.1.1] cluster core featuring two ligand-free, ' inverted tetrahedral' bridgehead silicon atoms, is described. Reactivity studies have provided evidence for both closed-shell and radical-type reactivity and have thus confirmed the unusual nature of the stretched silicon-silicon bond in the ' nonclassical' molecule.

(super 1)H, (super 31)P and (super 7)Li pulsed-gradient spin-echo (PGSE) diffusion and variable-temperature NMR results for THF solutions of the lithium and potassium salts derived from diphenylphosphino(o-cyanophenyl)aniline are described and compared to the solid-state results obtained by X-ray diffraction studies. The results reveal that, in solution, the salts favor mononuclear structures whereas in the solid state the data reveal dinuclear species.

The preparation of a set of new hydroxyphosphine pi-arene complexes is reported and it is shown that the distorted pi-arene-Ru interaction in new compounds adopts one structure in the solid state. Crystal structures of five new complexes are reported by using X-ray diffraction and NMR studies.

A series of new Ru(ll) arene phosphine complexes derived from Binap have been prepared. Specifically, reaction of Ru(OAc)2(Binap) with 3,5-(CF3)2C6H3)4B (BArF)·H(ORT2)2, is shown to afford new mono- and dinuclear Ru(ll) hydroxyphosphine π-arene complexes via a series of P-C bond cleavage reactions. The dinuclear Ru(ll) π-arene complexes contain bridging P(O)(OH)2 ligands. Crystal structures of five new complexes are reported and suggest an η4-arene rather than an η6-arene coordination mode. However, in solution, their 13C NMR data are more consistent with a strongly distorted η6-coordination mode. PGSE ¹H and 19F diffusion measurements on the dinuclear complexes suggest hydrogen bonding of the trifiate anion and ion-pairing of the BARF- anion. [ABSTRACT FROM AUTHOR]

The synthesis of C∧C∧P pre-ligands based on a dicyclohexylphosphine-substituted biphenyl framework is reported. The pre-ligands form the respective non-palindromic pincer complexes of Pt II and Pd II via double oxidative addition and subsequent comproportionation or C-H activation. The complexes of Pt II as well as Pd II emit similar green phosphorescence efficiently in the solid state, the former also in solution albeit with less intensity. The most fascinating photophysical feature, however, is a direct singlet-triplet (S 0 → T 1 ) excitation of this phosphorescence in the spectral window between the emission and the major singlet-singlet UV absorption. The S 0 → T 1 excitation spectra show a rich vibronic pattern, which is especially pronounced for the solid samples at cryogenic temperatures. The molar extinction of the lowest-energy singlet-triplet absorption band of the homologous Pt and Pd complexes as well as that of the Pt complex with a different (NHC) ancillary ligand were determined in tetrahydrofuran solutions. Quantum efficiencies of triplet formation (by intersystem crossing) via the "standard" excitation pathway S 0 → S n → T 1 were determined for the Pt complexes and found to be different in dependence of the ancillary ligand.

A straightforward access is provided to iron(II) complexes showing exceedingly slow spin-state interconversion by utilizing trigonal-prismatic directing ligands (L(n)) of the extended-tripod type. A detailed analysis of the interrelations between complex structure (X-ray diffraction, density functional theory) and electronic character (SQUID magnetometry, Mössbauer spectroscopy, UV/vis spectroscopy) of the iron(II) center in mononuclear complexes [FeL(n)] reveals spin crossover to occur along a coupled breathing/torsion reaction coordinate, shuttling the complex between the octahedral low-spin state and the trigonal-prismatic high-spin state along Bailar's trigonal twist pathway. We associate both the long spin-state lifetimes in the millisecond domain close to room temperature and the substantial barriers against thermal scrambling (Ea ≈ 33 kJ mol(-1), from Arrhenius analysis) with stereochemical constraints. In particular, the topology of the κ(6)N ligands controls the temporary and structural dynamics during spin crossover.