Main Group OM

Alkyl- and hydrido-bridges are both electron-deficient (3c-2e). They only differ in their sterics, and bridges with smaller ligands (hydrido) are preferred.

They are essentially "stabilized" carbanions which due to the negative charge react as strong nucleophiles or bases.

Many main-group organyls are very strong bases which exothermically react with water (moisture sensitive). The heat released can ignite them (pyrophoric) and/or the organic solvent they are stored in.

Bridges only form, when the complex fragments are electronically unsaturated. Electronically saturated complexes do not dimerize, etc. even if their ligands are small.

Alkyl and hydrido bridges are electron-deficient, while alkoxido bridges are sterically less favorable.

The number of carbonyl bands depends on the number of unique carbonyl ligands, which in turn is influenced by geometry and symmetry.

Organolithium compounds are the most reactive in this series, because they have the highest bond polarity (most ionic bond-character).

Protic solvents decompose organolithium species (acid-base reaction), and polar solvents tend to break higher aggregates apart through coordination to the electron-deficient Li-centers.

Carbonyl ligands are good pi-acceptors. Low valent metal centers provide sufficient electron density for favorable pi-backbonding to bound carbonyl ligands.