Tetraarylphenyls of the form 2,3,5,6-Ar4C6 (Ar = p-tert-butylphenyl) are investigated as sterically demanding ligands for the syntheses of compounds having two p-phenylene-bridged phosphorus centers. The precursor to such materials, 1,4-diiodo-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (1), is readily obtained via a one-pot procedure in 68% yield. Compound 1 is then used to provide the bis(dichlorophosphine) 1,4-bis(dichlorophosphino)-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (2) and the derived bis(phosphine) 1,4-bis(phosphino)-2,3,5,6-tetrakis(p-tert-butylphenyl)benzene (3) in yields of 56 and 94% respectively. These materials provide access to novel materials containing two low-coordinate phosphorus centers bridged by a sterically encumbered phenylene unit. Compound 2 reacts with benzaldehyde and 2,6-dichlorobenzaldehyde in the presence of excess trimethylphosphine and zinc to produce the new pale yellow crystalline bis(phosphaalkenes) (E,E)-PhC(H)=PAr4C6P=C(H)Ph (4a; 42%) and (E,E)-Ar'C(H)=PAr4C6P=C(H)Ar' (4b; 46%; Ar' = 2,6-dichlorophenyl). The crystal structure of 4a shows a P=C bond length of 1.676(5) A. Compound 2 is also used to provide the unusual red-orange bis(diphosphene) DmpP=PAr4C6P=PDmp (5; 55%; Dmp = 2,6-Mes2C6H3). Compound 5 is structurally characterized, and a P=P bond length of 2.008(2) A is ascertained.

The title complexes are stable, borate-bridged ansa-zirconocene species which have been prepared by reacting [{Ph(SMe2)B(η5-C5H4)2}ZrCl2] (1) with Cp*2AlMe and [PPN]Cl. Their molecular structures were determined by X-ray diffraction. Noteworthy are the stabilities of the borate−cyclopentadienyl linkages and the enhanced Lewis acidity of the boron within its strained ansa position.

The complex {Fe[HC(3,5-Me2pz)3]2}(BF4)2, shown crystallographically to contain a unique octahedral N6Fe site, shows a new type of spin-crossover behavior. The solid is high-spin from 350 K down to a temperature of 206 K, but below 206 K it undergoes a very abrupt decrease in magnetic moment. Mössbauer studies show conclusively that the magnetic moment change observed at 206−200 K arises from the complex changing over a very small temperature range from a high-spin state at higher temperatures to a mixture of high-spin and low-spin at lower temperatures, a mixture that does not change composition as the temperature is lowered to 5 K.

ansa-Calcocene compounds are effective reagents for the synthesis of ansa-chromocene complexes from CrCl 2 in the presence of a trapping ligand such as carbon monoxide or an isonitrile. A variety of ansa-chromocene carbonyl and tert-butyl isocyanide complexes have been prepared in this manner in high yields. The X-ray crystal structure of one of these complexes,CrCO, is described. Electrochemical studies on these complexes show that the isonitrile derivatives are more easily oxidized than the carbonyl derivatives. Preliminary examination of the reactivity of these complexes indicates that the nature of the substitution along the ethanediyl ansa-bridge influences the relative stabilities of the carbonyl complexes to oxidation in air, the ease with which the carbonyl ligands undergo substitution with tert-butyl isocyanide, and the relative sensitivities of the tert-butyl isocyanide adducts to photodecomposition. The ansa-bridge substitution also appears to influence the ability of the complexes to undergo structural changes, such as ring slippage, as revealed in their cyclic voltammograms.