Versatility of cyclooctatetraenyl ligands in rare earth metal complexes of the [M2(COT)3(THF)2] (M = Y and La) type

Two new organometallic cyclooctatetraenyl complexes of the type [M2(COT)3(THF)2] (M = Y and La) have been prepared, using optimized synthetic procedures, and fully characterized by X-ray diffraction analysis, IR and 1H NMR spectroscopies. The structures can be represented as formed by the double-decker [M(COT)2]- anion with an asymmetrically bound cationic [M(COT)(THF)2]+ unit. The COT rings in the anionic sandwich are not equidistant from the metal with the M-COTcentroid distances measuring at 1.991(5) Å and 2.074(5) Å for [Y(COT)2]-vs. 2.045(4) Å and 2.154(5) Å for [La(COT)2]-. The sandwich fragments are η2-coordinated to the second metal center with the average M-C distances of 2.837(4) Å and 2.879(5) Å for yttrium and lanthanum complexes, respectively. The M-COTcentroid distances in the cationic unit are 1.962(4) Å for the former and 2.009(2) Å for the latter.

One ligand fits all: lanthanide and actinide sandwich complexes comprising the 1,4-bis(trimethylsilyl)cyclooctatetraenyl (=COT′′) ligand

Twelve new lanthanide and actinide sandwich complexes containing the 1,4-bis(trimethylsilyl)cyclooctatetraenyl ligand (COT′′) have been prepared and structurally characterized by X-ray diffraction.

Rhenium(V) and Technetium(V) Complexes with Phosphoraneimine and Phosphoraneiminato Ligands

Air-stable rhenium(V) nitrido complexes are formed when [ReOCl3(PPh3)2], [NBu4][ReOCl4], or [NBu4][ReNCl4] are treated with an excess of silylated phosphoraneiminates of the composition Me3SiNPPh3 or Ph2P(NSiMe3)CH2PPh2 in CH2Cl2. Complexes of the compositions [ReNCl(Ph2PCH2PPh2NH)2]Cl (1), [ReN(OSiMe3)(Ph2PCH2PPh2NH)2]Cl (2) or [ReNCl2(PPh3)2] (3) were isolated and structurally characterized. The latter compound was also produced during a reaction of the rhenium(III) precursor [ReCl3(PPh3)2(CH3CN)] and Me3SiNPPh3. Nitrogen transfer from the phosphorus to the rhenium atoms and the formation of nitrido ligands were observed in all examples. All products of reactions with an excess of the potentially chelating phosphoraneiminate Me3SiNP(Ph2)CH2PPh2 contain neutral Ph2PCH2PPh2NH ligands. The required protons are supplied by a metal-induced decomposition of the solvent dichloromethane. The Re-N(imine) bond lengths (2.055-2.110 A) indicate single bonds, whereas the N-P bond with lengths between 1.596 A and 1.611 A reflect considerable double bond character. An oxorhenium(V) phosphoraneiminato complex, the dimeric compound [ReOCl2(mu-N-Ph2PCH2PPh2N)]2 (4), is formed during the reaction of [NBu4][ReOCl4] with an equivalent amount of Ph2P(NSiMe3)CH2PPh in dry acetonitrile. The blue neutral complex with two bridging phosphoraneiminato units is stable as a solid and in dry solvents. It decomposes in solution, when traces of water are present. The rhenium-nitrogen distances of 2.028(3) and 2.082(3) A are in the typical range of bridging phosphoraneiminates and an almost symmetric bonding mode. Technetium complexes with phosphoraneimine ligands were isolated from reactions of [NBu4][TcOCl4] with Me3SiNPPh3, and [NBu4][TcNCl4] with Me3SiNP(Ph2)CH2PPh2. Nitrogen transfer and the formation of a five-coordinate nitrido species, [TcNCl2(HNPPh3)2] (5), was observed in the case of the oxo precursor, whereas reduction of the technetium(VI) starting material and the formation of the neutral technetium(V) complex [TcNCl2(Ph2PCH2PPh2NH)] (6) or [TcNCl(Ph2PCH2PPh2NH)2]Cl (7) was observed in the latter case. Both technetium complexes are air stable and X-ray structure determinations show bonding modes of the phosphoraneimines similar to those in the rhenium complexes.

The syntheses and structures of lithium phosphinimide and phosphinimine complexes

The preparation and structures of [Li(µ-NPt-Bu3)]4 1, [Li(µ-Cl)(HNPt-Bu3)]4 2, and [Li(µ-Cl)(HNPPh3)]4 3 are described. The structure of 1 stands in contrast to that of the only other known Li-phosphinimide derivative, [Li(µ-NPPh3)]6. The impact of the steric bulk on the aggregation and the geometries of the Li4N4 and Li4Cl4 cores are considered and discussed.Key words: lithium compounds, phosphinimine, phosphinimide, P-N ligands.