In organometallic chemistry, A-frame complexes are coordination compounds that contain two bridging bidentate

ligand In coordination chemistry, a ligand is an ion or molecule ( functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's elec ...

s and a single atom bridge. They have the formula , where ''bd'' is a bidentate ligand like

dppm 1,1-Bis(diphenylphosphino)methane (dppm), is an organophosphorus compound with the formula CH2(PPh2)2. Dppm, a white, crystalline powder, is used in inorganic and organometallic chemistry as a ligand. It is more specifically a chelating ligand be ...

, and X and L are a wide variety of ligands. The term was coined to describe products arising from the oxidative addition to Rh(I)Rh(I) complexes.

Scope of compounds

A-frame complexes typically consist of a pair of square-planar metal centres. Consequently, this family of complexes is found for those metals that tend to adopt that geometry, Rh, Ir, Ni, Pd, Pt, and Au. In addition to dppm, the analogous tetramethyldiphosphine (dmpm) also forms such complexes as do some related ligands, such as diphenyl-2-pyridylphosphine. The bridging site can be occupied by a variety of ligands, including CO, SO, NO, CH₂,

hydride In chemistry, a hydride is formally the anion of hydrogen( H−). The term is applied loosely. At one extreme, all compounds containing covalently bound H atoms are called hydrides: water (H2O) is a hydride of oxygen, ammonia is a hydride ...

, and chloride. Pd2Cl2(CO)(dppm)2

Preparation

A frame complexes are often produced by the addition of reagents of the type AX₂ to low valent complexes of dppm: :2 M(0) + AX₂ + 2 dppm → M₂(μ-A)(dppm)₂X₂ Alternatively the group "A" can be added across a preformed M-M bond, as indicated by the

oxidative addition Oxidative addition and reductive elimination are two important and related classes of reactions in organometallic chemistry. Oxidative addition is a process that increases both the oxidation state and coordination number of a metal centre. Oxid ...

of elemental sulfur:Tetsuro Murahashi, Hideo Kurosawa "Organopalladium complexes containing palladium/palladium bonds" Coordination Chemistry Reviews 2002, volume 231, pp. 207-228. {{doi, 10.1016/S0010-8545(02)00121-2 :Pd₂(dppm)₂Cl₂ + S → Pd₂(μ-S)(dppm)₂Cl₂

References

Coordination complexes