Pentamethyltantalum is a

homoleptic In inorganic chemistry, a homoleptic chemical compound is a metal compound with all ligands identical. The term uses the " homo-" prefix to indicate that something is the same for all. Any metal species which has more than one type of ligand is he ...

organotantalum compound. It has a propensity to explode when it is melted. Its discovery was part of a sequence that lead to

Richard R. Schrock Richard Royce Schrock (born January 4, 1945) is an American chemist and Nobel laureate recognized for his contributions to the olefin metathesis reaction used in organic chemistry. Education Born in Berne, Indiana, Schrock went to Mission Bay H ...

's Nobel Prize discovery in

olefin metathesis Olefin metathesis is an organic reaction that entails the redistribution of fragments of alkenes (olefins) by the scission and regeneration of carbon-carbon double bonds. Because of the relative simplicity of olefin metathesis, it often create ...

Production

Pentamethyltantalum can be made from the reaction of methyllithium with Ta(CH₃)₃Cl₂. Ta(CH₃)₃Cl₂ is in turn made from

tantalum pentachloride Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantal ...

and

dimethylzinc Dimethylzinc, also known as Zinc methyl, DMZ, or DMZn is a colorless volatile liquid Zn(CH3)2, formed by the action of methyl iodide on zinc at elevated temperature or on zinc sodium alloy. :2Zn + 2CH3I → Zn(CH3)2 + ZnI2 The sodium assists the ...

. The preparation was inspired by the existence of pentaalkyl compounds of phosphorus and arsenic, and the discovery of

hexamethyltungsten Hexamethyltungsten is the chemical compound Tungsten, W(Methyl, CH3)6 also written WMe6. Classified as a transition metal alkyl complexes, transition metal alkyl complex, hexamethyltungsten is an air-sensitive, red, crystalline solid at room tempe ...

. The discoverer,

considered tantalum to be a metallic phosphorus, and tried the use of methyllithium.

Properties

The pentamethyltantalum adopts a

square pyramid In geometry, a square pyramid is a pyramid having a square base. If the apex is perpendicularly above the center of the square, it is a right square pyramid, and has symmetry. If all edge lengths are equal, it is an equilateral square pyramid, ...

shape. Ignoring the C-H bonds, the molecule has ''C''_4v symmetry. The four carbon atoms at the base of the pyramid are called basal, and the carbon atom at the top is called apical or apex. The distance from tantalum to the apical carbon atom is 2.11 Å, and to the basal carbon atoms is 2.180 Å. The distance from hydrogen to carbon in the methyl groups is 1.106 Å. The angle subtended by two basal carbon bonds is 82.2°, and the angle between the bonds to the apex and a carbon on the base is about 111.7°. At room temperature pentamethyltantalum can spontaneously explode, so samples are stored below 0°.

Reactions

With many carbon-hydrogen bonds near Ta, analogues of pentamethyltantalum are susceptible to alpha elimination. Excess methyllithium reacts to yield higher coordinated methyl tantalum ions a(CH₃)₆sup>− and a(CH₃)₇sup>2−. Pentamethyltantalum in solution forms stable insoluble complex material when mixed with

dmpe 1,2-Bis(dimethylphosphino)ethane (dmpe) is a diphosphine ligand in coordination chemistry. It is a colorless, air-sensitive liquid that is soluble in organic solvents. With the formula (CHPMe), dmpe is used as a compact strongly basic spectator l ...

(CH₃)₂PCH₂CH₂P(CH₃)₂. With

nitric oxide Nitric oxide (nitrogen oxide or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes denoted by a dot in its che ...

it gives a white coloured dimer with formula ₂ (Me=CH₃).

References

{{tantalum compounds Organometallic compounds Tantalum compounds Methyl complexes