An organotransition-metal complex with pentagonal-pyramidal structure

Star gazing: The six-coordinate organoniobium(V) compound [NBu(4) ](2) [NbO(C(6) F(5) )(5) ] has been found to exhibit a pentagonal-pyramidal (PPY-6) structure, which is unprecedented in organotransition-metal chemistry (see picture: complex as viewed down the O-Nb axis; C in gray, O in red, F in yellow, and Nb in blue).     

Stepwise Degradation of Trifluoromethyl Platinum(II) Compounds

The action of moisture on the homoleptic organoplatinum(II) compound [NBu₄]₂[Pt(CF₃)₄] ( 1 ) gives rise to the carbonyl derivative [NBu₄][Pt(CF₃)₃(CO)] ( 2 ), which is itself moisture stable. However, treatment of compound 2 with HCl(aq) results in the formation of [NBu₄][cis‐Pt(CF₃)₂Cl(CO)] ( 3 ), which undergoes degradation of an additional CF₃ group by further treatment with HCl(aq) in large excess, affording [NBu₄][cis‐Pt(CF₃)Cl₂(CO)] ( 4 ). The carbonyl derivatives 2 – 4 are fairly stable species, in which the CO ligand, however, can be readily extruded by reaction with trimethylamine N‐oxide (ONMe₃). Thus, compound 2 reacts with ONMe₃ in the presence of a number of neutral or anionic ligands affording a series of singly or doubly charged derivatives with the general formulae [NBu₄][Pt(CF₃)₃(L)] [L=CNtBu ( 5 ), PPh₃ ( 6 ), P(o‐tolyl)₃ ( 7 ), tht ( 8 ; tht=tetrahydrothiophene)] and [NBu₄]₂[Pt(CF₃)₃X] [X=Cl ( 9 ), Br ( 10 ), I ( 11 )], respectively. Compound 2 also reacts with ONMe₃ and pyridin‐2‐thiol (C₅H₅NS) giving rise to the five‐membered metallacyclic derivative [NBu₄][Pt(CF₃)₂(CF₂NC₅H₄S‐κC,κS)] ( 12 ), which can be viewed as a difluorocarbene species stabilized by intramolecular base coordination. On the other hand, treatment of compound 3 with ONMe₃ in the presence of C₅H₅NS yields the four‐membered metallacyclic compound [NBu₄][Pt(CF₃)₂(NC₅H₄S‐κN,κS)] ( 13 ). The geometries of the metallacycles in compounds 12 and 13 are compared. In the absence of any additional ligand, compound 3 undergoes dimerization producing the dinuclear species [NBu₄]₂[{Pt(CF₃)₂}₂(μ‐Cl)₂] ( 14 ). Halide abstraction in the latter compound with AgClO₄ in THF yields the solvento compound cis‐[Pt(CF₃)₂(thf)₂] ( 15 ). The highly labile character of the THF ligands in compound 15 makes this species a convenient synthon of the “cis‐Pt(CF₃)₂” unit.     

M−C Bond Homolysis in Coinage‐Metal [M(CF3)4]− Derivatives

A comparative study of the homoleptic [M(CF₃)₄]^? complexes of all three coinage metals (M=Cu, Ag, Au) reveals that homolytic M?C bond cleavage is favoured in every case upon excitation in the gas phase (CID‐MS²). Homolysis also occurs in solution by photochemical excitation. Transfer of the photogenerated CF₃^. radicals to both aryl and alkyl carbon atoms was also confirmed. The observed behaviour was rationalized by considering the electronic structure of the involved species, which all show ligand‐field inversion. Moreover, the homolytic pathway constitutes experimental evidence for the marked covalent character of the M?C bond. The relative stability of these M?C bonds was evaluated by energy‐resolved mass spectrometry (ERMS) and follows the order Cu<Ag?Au. The qualitatively similar and rather uniform behaviour experimentally observed for all three coinage metals gives no ground to suggest variation in the metal oxidation state along the group.     

The first structurally characterised homoleptic sigma-organotitanium(III) compound

The paramagnetic [EPR, S = 1/2, d1; gav = 1.959(2)] organotitanate(III) anion [TiIII(C6Cl5)4] has been found to be a mononuclear species with nearly tetrahedral geometry (X-ray).     

A hexanuclear gold carbonyl cluster

The hexanuclear gold carbonyl cluster [PPh₄]₂[Au₆(CF₃)₆Br₂(CO)₂] (4) has been obtained by spontaneous self-assembly of the following independent units: CF₃AuCO (1) and [PPh₄][Br(AuCF₃)₂] (3). The cyclo-Au₆ aggregate 4, in which the components are held together by unassisted, fairly strong aurophilic interactions (Au···Au ∼310 pm), exhibits a cyclohexane-like arrangement with chair conformation. These aurophilic interactions also result in significant ν(CO) lowering: from 2194 cm^–1 in the separate component 1 to 2171 cm^–1 in the mixed aggregate 4. Procedures to prepare the single-bridged dinuclear component 3 as well as the mononuclear derivative [PPh₄][CF₃AuBr] (2) are also reported.