Dative, or nonoxidative, ligand coordination is common in transition metal complexes; however, this bonding motif is rare in compounds of main group elements in the formal oxidation state of zero. Here, we report that the potassium graphite reduction of the neutral hypervalent silicon-carbene complex L:SiCl4 {where L: is:C[N(2,6-Pri2-C6H3)CH]2 and Pri is isopropyl} produces L:(Cl)Si-Si(Cl):L, a carbene-stabilized bis-silylene, and L:Si=Si:L, a carbene-stabilized diatomic silicon molecule with the Si atoms in the formal oxidation state of zero. The Si-Si bond distance of 2.2294 +/- 0.0011 (standard deviation) angstroms in L:Si=Si:L is consistent with a Si=Si double bond. Complementary computational studies confirm the nature of the bonding in L:(Cl)Si-Si(Cl):L and L:Si=Si:L.

The syntheses and molecular structures of four compounds are reported:  1 (RBBr3), 2 (R(H)2B−B(H)2R), 3 (R(H)BB(H)R), and 4 (RBH3) (R = :C{N(2,6-Pr i 2C6H3)CH}2). These compounds were characterized by single-crystal X-ray diffraction, 1H and 11B NMR, and elemental analyses. Compounds 2 and 3 were prepared by the KC8 reduction of 1 in Et2O. Compound 3 is the first structurally characterized neutral diborene (mean BB:  1.560(18) Å). The nature of the BB double bond in 3 was delineated by DFT computations.

The potassium graphite reduction of L:PCl3 leads to the formation of carbene-stabilized diphosphorus molecules, L:P-P:L, 1 (L: = :C{N(2,6-Pri2C6H3)CH}2) and 2 (L: = :C{N(2,4,6-Me3C6H2)CH}2), respectively. The nature of the bonding in 1 and 2 was delineated by DFT computations.

General principles for designing stable highly symmetrical clusters are proposed. This approach takes advantage of both the extra stability of cage aromaticity and the good geometrical balance between the outer cage and the endohedral atom. The applicability of these design principles was confirmed by gas-phase experimental observations on group 14 element cages with endohedral Al's and also is illustrated by many literature examples of diverse systems.

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Candidates for the lowest energy structures of medium-sized Au(n), n = 32, 38, 44, 50, and 56, clusters were evaluated using gradient-corrected DFT computations. Both hollow cage and space-filling conformations were considered. The cages were constructed using fullerene-based templates. The space-filling structures were generated by employing a genetic algorithm. We have found that the space-filling isomers were lower in energy except for two notable cases. Like Au(32) [Johansson, M. P.; Sundholm, D.; Vaara, J. Angew. Chem. Int. Ed. 2004, 43, 2678], a hollow cage configuration of Au(50) is more stable than its alternative space-filling isomeric forms. The unusual stabilities of the cage Au(32) and Au(50) can be attributed to spherical aromaticity; both exhibit large negative nucleus-independent chemical shifts and exceptionally large HOMO-LUMO gaps.

Photolysis of the tetrahedrane Fe2(CO)6(mu-S2) at 450 +/- 35 nm in a Nujol matrix at low temperatures gives an isomer characterized by its nu(CO) infrared frequencies. Comparison of these experimental frequencies with those calculated by density functional theory using the BP86 functional indicates this photoisomer to be the butterfly singlet diradical Fe2(CO)6S2 isomer in which the S-S bond of the tetrahedrane is broken but the Fe-Fe bond is retained. Photolysis at higher energies (420-280 nm) results in CO loss from this singlet butterfly diradical as indicated again by comparison of the experimental infrared nu(CO) frequencies with those calculated for an Fe2(CO)5S2 isomer of this type.

Metal carbonyls have been known for over 75 years. Within the last 40 years numerous anionic derivatives of metal carbonyls have been synthesized. More recently some of these metal carbonyl anions have been used as intermediates of the synthesis of unusual organometallic compounds. This Account summarizes some