Fluorescence techniques have been used to identify humic substances, (e.g. aquatic fulvic acids from different origins). Synchronous scans have proven adequate for distinguishing detail and differentiating samples. As well, fluorescence has often been used to probe humic interactions with metals and xenobiotic organics. In this study, the fluorescence of a well-characterized material, Laurentian fulvic acid (LFA) was compared with that of a simple hydroquinone/quinone (H 2 Q/Q) model system. Synchronous fluorescence (room T) and laser-excited fluorescence experiments at 10°K were carried out to characterize the fluorophore. The synchronous fluorescence behavior of LFA displayed similarities to that of an equilibrated, aerated, H 2 Q/Q system, but only at higher pH. (Higher pH favours a shift of the redox equilibrium towards quinone.) In contrast, the spectra of LFA suggest the role of "quinone" groups, even at lower pH. A signif- Aquatic Sciencesicant feature of these spectra is a lowest energy band. At low temperature this band was more selectively excited at 470 nm, but vibrationally resolved line narrowed spectra were not observed. Fluorescence lifetimes were very short compared to the laser pulse width of ca. 10 ns. Under the low T condition the spectra of LFA and the model are essentially identical. We suggest that the principal luminophore in LFA is a quinone-hydroquinone type, perhaps a charge transfer complex consistent with the absence of the fluorescence line-narrowing phenomenon. The spectra imply a lowest energy component of LFA emission from a fluorophore very similar to that of the simplest H 2 Q/Q. The significant similarities of the model system to LFA are underscored by striking parallels in the radicals in the two systems seen in well-resolved electron paramagnetic resonance (EPR) spectra that could be obtained at pH = 6.

The copper-catalyzed Click reaction of phenyl azide with ethynylphosphine oxides provides new P-substituted triazoles. With tris(ethynyl)phosphine oxide this route affords a versatile scorpionate ligand that coordinates to RhCl 3 as a tripodal N ligand. Upon reduction, the same ligand can act as a P donor to W(CO) 5 . Both coordination modes can be combined, giving access to a bimetallic Mo/W complex.

Novel transient phosphinidene complex Ph−PMo(CO)4PMe3, generated from a 7-phosphanorbornadiene precursor, adds to CC and C⋮C bonds to give Mo(CO)4PMe3-complexed phosphiranes and phosphirenes. The cis-PMe3 ligand weakens the interaction between the molybdenum complex and the three-membered ring. Under mild CO pressure the Mo(CO)4PMe3 transition metal group detaches from the phosphorus center of the ring structure by selective CO substitution. The resulting byproduct Mo(CO)5PMe3 can be reused in the synthesis of the phosphinidene precursor.

Intramolecular phosphinidene addition to the C==C bond of Mo-complexed, seven-membered phosphorus heterocycles affords three novel [(diphos)Mo(CO)(4)] complexes (18-20). The three bidentate phosphorus baskets differ in the composition of the seven-membered ring: one of the phosphorus atoms is flanked by CH(2), NCH(3), or O. The unsaturated tetrahydrophosphepine precursors are synthesized by either ring-closing metathesis (C and N derivatives) or by a cyclization sequence (O derivative). The crystal structures of the nitrogen- (19) and oxygen-containing (20) baskets have relatively small P-Mo-P angles of 76.240(13) degrees and 77.626(12) degrees , respectively, and complex 20 has slightly shortened Mo--P bond lengths.

The natural product Gramicidin S is a promising scaffold for novel oligopeptide-based bisphosphine ligands, combining the advantageous rigid chiral backbone with the close proximity of phosphine substituents. The required unnatural, phosphine-containing, amino acid building blocks were synthesized by means of a novel protocol that involves the enantioselective alkylation of a chiral nickel Schiff base template. Three Ni complexes were prepared with different alkyl chains between the phosphine group and the alpha-carbon atom of the incorporated glycine; the absolute stereochemistry of two of them was determined by single-crystal X-ray structure analysis. By detaching the template, enantiopure L-phosphine amino acids resulted enabling the solid-phase, stepwise construction of a linear sequence of the phosphine-modified oligopeptides. On cyclization three bisphosphine-substituted Gramicidin S analogues resulted, differing only in the size and shape of the linkage between the phosphine groups and the oligopeptides backbone. Their crystal structures suggest these species to have potential as chelating ligands.

Phosphorus-based macrocycles with acetylenic scaffolds have been built from acetylene-substituted phosphane oxides that were formed from diisopropylphosphoramidic dibromide (3) and an acetylenic Grignard reagent. The fourand six-edged macrocycles 15 and 16, in which the iPr 2 NP(O) units are connected through 1,3-butadiyne rods, were obtained from the monosilylated derivative of iPr 2 NP(O)(C 2 H) 2 (7) by multiple acetylene coupling reactions under oxidative

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Heating the nonchelating cis-bis-7-phosphanorbornadiene-[Mo(CO)4] complex (13) results in the thermal decomposition of one of the 7-phosphanorbornadiene groups. The phosphinidene thus generated adds intramolecularly to a C=C bond of the other ligand to give the novel diphosphorus complex 14. This reaction constitutes a metal-template-directed synthesis. Likewise, the intramolecular phosphinidene addition to the C=C bond of a Mo-phospholene ligand affords the diphos complex 18. Its crystal structure exhibits an extremely small P-Mo-P bite-angle for a five-membered chelate ring. The similar intramolecular 1,2-addition to a C=C bond of a phosphole ligand gives a highly strained, unstable intermediate product. Scission of its P-Mo bond generates a free coordination site, which is then occupied by either CO or a phosphole to yield complexes 22 and 23, respectively. The analogous intermolecular addition of [PhPW(CO)5] to a [phosphole-W(CO)5] complex gives the di-[W(CO)5] complexed adduct 28. The directing effect of the metal on the intra- and intermolecular additions is discussed.