Muon implantation of metallocenes: ferrocene

Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17 T, for the low-temperature phase at 18 K. The high-temperature phase at 295 K shows that only the last feature shifted down to about 0.49 T and a muon spin relaxation peak at about 0.106 T which approaches zero field when reaching the phase transition temperature of 164 K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe-Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the muSR spectra of ferrocene was estimated to be 584 K. Correlation time for the ring rotation dynamics of the Fe-Mu radical at this temperature is 3.2 ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported.     

Unequivocal structural assignment of the product of methylation of 4-nitro-5-styrylimidazole

The structure of one of the two regioisomeric products of methylation of 4-nitro-5-styrylimidazole has been assigned by single-crystal X-ray diffraction analyses.     

Crystal structure of 5,10-(diphenyl)-5,10-dihydrophenarsazine

The crystal structure of the title compound 1 , the first phenarsazine possessing a 10-phenyl substituent to be synthesized, has been determined by single crystal x-ray methods. The crystals are monoclinic, space group P2₁/c with four molecules in a cell of dimensions a = 10.737(3), b = 8.561(4), c = 20.523(7)Å, β = 91.91(3)° and V = 1885(1)ų. The structure has been refined by full matrix least-squares to R = 0.046 using 2087 observed reflections. The folding angle between the two benzo planes is 151.7(4)° indicating that 1 is significantly more puckered than phenarsazines substituted with 5-aryl groups. Moreover, although both phenyl groups adopt a boat-axial conformation, the planes of the aryl rings are nearly perpendicular to each other with the 10-phenyl group adopting the usual conformation (i.e. in the plane bisecting the phenarsazine ring which contains As(5) and N(10)) and the 5-phenyl group assuming the a typical conformation (i.e. very nearly perpendicular to the plane bisecting phenarsazine ring). The bond distance between As and the carbon atom of the 5-phenyl ring is approximately the same as that found in other 5-arylphenarsazine compounds indicating little resonance interactions between As and the aromatic ring in 1 .     

Muonium Chemistry at Diiron Subsite Analogues of [FeFe]‐Hydrogenase

The chemistry of metal hydrides is implicated in a range of catalytic processes at metal centers. Gaining insight into the formation of such sites by protonation and/or electronation is therefore of significant value in fully exploiting the potential of such systems. Here, we show that the muonium radical (Mu^.), used as a low isotopic mass analogue of hydrogen, can be exploited to probe the early stages of hydride formation at metal centers. Mu^. undergoes the same chemical reactions as H^. and can be directly observed due to its short lifetime (in the microseconds) and unique breakdown signature. By implanting Mu^. into three models of the [FeFe]‐hydrogenase active site we have been able to detect key muoniated intermediates of direct relevance to the hydride chemistry of these systems.     

Reactions of a Cyclenphosphoranide Platinum (II) Complex and the Role of Highly Nucleophilic Substituents at the Axial Positions of a Trigonal Bipyramid

Abstract

(η²-cyclenP)Pt(Cl)PPh₃ 1 exhibits a large variety of selective reactions due to the platinum metal and cyclenphosphoranide ligand, cyclenP. Moreover, the cyclenP ligand is capable of altering many of the usual reactions and/or mechanisms at square planar platinum (II) complexes.