Chromium, iron, ruthenium and gold complexes of 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-phenylallene: A versatile ligand

Successive treatment of 9-(phenylethynyl)fluoren-9-ol (1a), with HBr, butyllithium and chlorodiphenylphosphine furnishes 3,3-(biphenyl-2,2′-diyl)-1-diphenylphosphino-1-phenylallene (5). Moreover, reaction of 1a directly with chlorodiphenylphosphine yields the corresponding allenylphosphine oxide (6). The allenylphosphine (5), and Fe₂(CO)₉ initially form the phosphine-Fe(CO)₄ complex, 11, which is very thermally sensitive and readily loses a carbonyl ligand. In the resulting phosphine-Fe(CO)₃ system, 12, the additional site at iron is coordinated by the allene double bond adjacent to phosphorus; the Fe(CO)₃ tripod in 12 exhibits restricted rotation on the NMR time-scale even at room temperature. The corresponding chromium complex, (5)-Cr(CO)₅ (9), has also been prepared. The gold complexes (5)-AuCl (13), and [(5)-Au(THT)]⁺ X⁻, where (THT) is tetrahydrothiophene, and X = PF₆ (14a), or ClO₄ (14b), are analogous to the known triphenylphosphine-gold complexes. In contrast, in the (arene)(allenylphosphine)RuCl₂ system the allene double bond adjacent to phosphorus displaces a chloride, and the resulting cationic species undergoes nucleophilic attack by water yielding ultimately a five-membered Ru-P-CC-O ruthenacycle (17). Thus, the allenylphosphine (5), reacts initially as a conventional mono-phosphine but, when the metal centre has a readily displaceable ligand such as a carbonyl or halide, the allene double bond adjacent to the phosphorus can also function as a donor. X-ray crystal structures are reported for 5, 6, 11, 12, 13, 14a, 14b and 17.     

Spin-glass, antiferromagnetism and kondo behavior in Ce2Au1−x Co x Si3 alloys

Recently, the solid solution Ce₂Au_{1− x Co} xSi₃ has been shown to exhibit many magnetic anomalies associated with the competition between magnetic ordering and the Kondo effect. Here we report high pressure electrical resistivity of Ce₂AuSi₃, ac susceptibility (X) and magnetoresistance of various alloys of this solid solution in order to gain better knowledge of the magnetism of these alloys. High pressure resistivity behavior is consistent with the proposal that Ce₂AuSi₃ lies at the left-hand side of the maximum in Doniach’s magnetic phase diagram. The ac X data reveal that there are in fact two magnetic transitions, one at 2 K and the other at 3 K for this compound, both of which are spin-glass-like. However, as the Co concentration is increased, antiferromagnetism is stabilized for intermediate compositions before attaining non-magnetism for the Co end member.     

Sequential formation of yellow, red, and orange 1-phenyl-3,3-biphenylene-allene dimers prior to blue tetracene formation: Helicity reversal in trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane

1-Phenyl-3,3-biphenyleneallene (2), the base-catalyzed rearrangement product of 9-phenylethynylfluorene (1) yields a yellow, head-to-tail dimer 6 that, upon gentle warming, is converted to the red tail-to-tail isomer trans-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (7), in which the two fluorenylidene moieties severely overlap. The helical sense of the fluorenylidene moieties in 7 matches that of the phenyl substituents, and the interplanar angle between the fluorenylidene moieties is 41 degrees . At 80 degrees C, 6 isomerizes to orange cis-3,4-diphenyl-1,2-bis(fluorenylidene)cyclobutane (8), which at 110 degrees C is converted to orange trans diastereomer 9, whereby the helicity of the overlapping fluorenylidene moieties is reversed from that in 7 such that they are aligned with the ring hydrogen atoms, and the interplanar angle between the fluorenylidene moieties is now 60 degrees . At 180 degrees C, 6 rearranges to dispirodihydrotetracene 3 and blue, electroluminescent diindenotetracene 4, which is readily oxidized to peroxide 5. In the solid state, both 3 and 4 adopt structures with Ci symmetry (only an inversion center) such that the central polycyclic framework is nonplanar. Deprotonation of yellow head-to-tail allene dimer 6 with tBuOK in DMSO and reprotonation with HOAc yields the [1,3]-hydrogen migration product 10, in which the proton originally on the cyclobutane ring is now sited at C9 on the exocyclic fluorenyl substituent. Analogously, deprotonation and reprotonation of orange dimer 9 furnishes [1,3]-hydrogen migration product 11. Side product 17, formed during the synthesis of 1 from 9-phenylethynylfluoren-9-ol, BF3 and Et3SiH, was shown to be a silyl-indene spiro-linked to C9 of fluorene. All products were characterized by NMR spectroscopy and X-ray crystallography, and the mechanisms of these interconversions are discussed.     

The growth of a single crystal of Sr3CuIrO6 and its magnetic behavior compared to polycrystals

We have grown single crystals of the psuedo-one-dimensional compound Sr₃CuIrO₆, a K₄CdCl₆-derived monoclinic structure with Cu-Ir chains along the [101] direction. We present the ac and dc magnetization behavior of the single crystals in comparison with that of the polycrystalline form reported earlier. There is a distinct evidence for at least two magnetic transitions, at 5 K (T ₁) and 19 K (T ₂), with different relative magnitudes in the single and polycrystals. The low temperature magnetic relaxation behavior of both the forms is found to be widely different, exhibiting unexpected time dependence.