The free energies for hydride donation (ΔG M + ) have been determined in acetonitrile solution for a series of seven molybdenum and tungsten compounds (1−7) of general formula (C5R5)M(CO)2(L)H, which yield the salts [(C5R5)M(CO)2(L)(NCMe)][BF4] in these reactions. These data constitute the first thermodynamic data for hydride transfer by transition metal hydrides, and were gathered from equilibrium studies with carbenium ion salts of known hydride ion affinities in acetonitrile. The metal hydride ΔG M + values range from ca. 79 to 89 kcal/mol, and these values may be compared with pK as for related compounds to demonstrate that proton-transfer processes are somewhat more sensitive to changes in co-ligands than are hydride transfer processes. Additionally, kinetic studies of hydride transfer reactions with hydride acceptor [(p-MeOPh)2CPh][BF4] exhibit second-order rate constants ranging from ca. 200 to 7500 M-1 s-1. These rates show a correlation with thermodynamic driving force, and a Brönsted plot yields a slope of 0.20. The thermodynamic data may be used in conjuction with the appropriate thermodynamic cycles to calculate energies for various processes in which compounds such as 1−7 are known to function as hydride donors.

Laboratory experiments that produced tholins in a simulated Titan atmosphere were conducted. We report the first systematic analyses of these compounds using Fourier-transform ion cyclotron resonance mass spectrometry. The findings suggest surprising simplicity and nonrandomness in the mass distribution and regularity in species clusters. The degree of unsaturation generally increased with increasing molecular weight in a predictable fashion, and nitrogen is proposed as the dominant carrier of unsaturation. In detected compounds with a general formula of C(x)H(y)N(z), the carbon to nitrogen ratio (x/z) varied only slightly within a narrow limit, and decreased with increasing molecular weights. These compounds are of potential prebiotic interest since they sediment to the surface of Titan, and would dissolve readily in transient aqueous pools that might be generated from time to time by impacts and volcanic

Two general routes to binucleating bis(amidinate) ligands based on dibenzofuran and 9,9-dimethylxanthene backbones are reported. The free-base form of one of the ligands, (Ph,Mes)L(DBF)H(2), forms a 1:1 adduct with acetone. Single-crystal X-ray diffraction of this adduct reveals bidentate H-bonding of the bis(amidine) to the ketone oxygen. Bond lengths suggest that the individual H-bonds are relatively weak, yet IR spectroscopy shows a significant -26 cm(-1) shift for the carbonyl stretch relative to free acetone. Additionally, the new dialuminum complexes (i)(Pr)L(DBF)Al(2)Me(4) (3), (i)(Pr)L(Xan)Al(2)Me(4) (4), (t)(Bu,Et)L(DBF)Al(2)Me(4) (5), and (t)(Bu,Et)L(Xan)Al(2)Me(4) (6) are prepared by reaction of Al(2)Me(6) with the bis(amidines) in toluene solution. (1)H NMR spectroscopic studies indicate that 3 and 4 interact weakly with certain Lewis bases (DMSO, DMF, pyridine) to effect the exchange of the Al-bound Me groups. Other bases, such as THF and TMEDA, fail to interact. Solid-state structures for 3 and 4 are reported.

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