Carbene analogs in

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

are

carbenes In organic chemistry, a carbene is a molecule containing a neutral carbon atom with a valence of two and two unshared valence electrons. The general formula is or where the R represents substituents or hydrogen atoms. The term "carbene" may ...

with the

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

atom replaced by another

chemical element A chemical element is a chemical substance whose atoms all have the same number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8: each oxygen atom has 8 protons in its ...

. Just as regular carbenes they appear in

chemical reactions A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products ...

as reactive intermediates and with special precautions they can be stabilized and isolated as chemical compounds. Carbenes have some practical utility in

organic synthesis Organic synthesis is a branch of chemical synthesis concerned with the construction of organic compounds. Organic compounds are molecules consisting of combinations of covalently-linked hydrogen, carbon, oxygen, and nitrogen atoms. Within the gen ...

but carbene analogs are mostly laboratory curiosities only investigated in academia. Carbene analogs are known for elements of

group 13 The Group 13 network (, ) was a Jewish collaborationist organization in the Warsaw Ghetto during the German occupation of Poland in World War II. The rise and fall of the Group was likely a proxy for power struggles between various facti ...

, group 14,

group 15 , - ! colspan=2 style="text-align:left;" , ↓ Period , - ! 2 , , - ! 3 , , - ! 4 , , - ! 5 , , - ! 6 , , - ! 7 , , - , colspan="2", ---- ''Legend'' A pnictogen ( or ; from "to choke" and -gen, "generator") is any ...

and

group 16 The chalcogens (ore forming) ( ) are the chemical elements in group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellurium (Te), and the ...

Group 13 carbene analogs

In group 13 elements the

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

carbene analog is called a

borylene A borylene is the boron analogue of a carbene. The general structure is R-B: with R an organic moiety (chemistry), moiety and B a boron atom with two unshared electrons. Borylenes are of academic interest in organoboron chemistry. A diradical, sin ...

or boranylidene.

Group 14 carbene analogs

The heavier group 14 carbenes are

silylene Silylene is a chemical compound with the formula SiR2. It is the silicon analog of carbene. Silylene rapidly when condensed. Silylenes are formal derivatives of silylene with its hydrogens replaced by other substituents. Most examples feature ...

s, R₂Si:, germylenes R₂Ge: (example diphosphagermylene), stannylenes R₂Sn: and plumbylenes R₂Pb:, collectively known as metallylenes and regarded as

monomer A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization. Classification Chemis ...

s for polymetallanes. The

oxidation state In chemistry, the oxidation state, or oxidation number, is the hypothetical Electrical charge, charge of an atom if all of its Chemical bond, bonds to other atoms are fully Ionic bond, ionic. It describes the degree of oxidation (loss of electrons ...

for these compounds is +2 and stability increases with

principal quantum number In quantum mechanics, the principal quantum number (''n'') of an electron in an atom indicates which electron shell or energy level it is in. Its values are natural numbers (1, 2, 3, ...). Hydrogen and Helium, at their lowest energies, have just ...

(moving down a row in the

periodic table The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows (" periods") and columns (" groups"). It is an icon of chemistry and is widely used in physics and other s ...

). This makes dichloroplumbylene PbCl₂ and dichlorostannylene SnCl₂ stable

ionic compound In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions (Cation, cations) and negatively charged ions (Anion, anions), which results in a compound with no net electric charge (electrica ...

s although they exist as polymers or ion pairs. Group 14 carbene analogs do not form hybrid orbitals but instead retain (ns)²(np)² electron configuration due to the increasing s p gap for larger elements. Two electrons remain in an s-orbital and therefore their compounds have exclusively singlet ground states and not the triplet ground state which can be observed in carbenes depending on the substituents. The s-orbital (

lone pair In chemistry, a lone pair refers to a pair of valence electrons that are not shared with another atom in a covalent bondIUPAC ''Gold Book'' definition''lone (electron) pair''/ref> and is sometimes called an unshared pair or non-bonding pair. Lone ...

) is inert and the vacant

p-orbital In quantum mechanics, an atomic orbital () is a function describing the location and wave-like behavior of an electron in an atom. This function describes an electron's charge distribution around the atom's nucleus, and can be used to calc ...

is very reactive. Stable group 14 carbenes require stabilization of this p-orbital which is usually accomplished by coordination of a Cp* ligand or coordination to

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

phosphorus Phosphorus is a chemical element; it has Chemical symbol, symbol P and atomic number 15. All elemental forms of phosphorus are highly Reactivity (chemistry), reactive and are therefore never found in nature. They can nevertheless be prepared ar ...

containing ligands, although stabilization can be achieved through steric protection alone. General methods for the synthesis of carbon-substituted (

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

) metallylenes are reduction of M⁴⁺ species or

substitution reaction A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ar ...

s at M²⁺ halides. Stable metallylenes require bulky substituents in order to prevent nucleophilic attack of the metal center at the p-orbital. Examples of these bulky substituents in R₂M: are mesityl, Dis (di(trimethylsilyl)methyl) and

adamantyl Adamantane is an organic compound with formula C10H16 or, more descriptively, (CH)4(CH2)6. Adamantane molecules can be described as the fusion of three cyclohexane rings. The molecule is both rigid and virtually stress-free. Adamantane is the mo ...

groups. With insufficient steric shielding the metallylene will form a dimer or a

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

. The first isolable dialkylgermylene was synthesised in 1991: :Me₅C₅GeCl + LiCH(Si(Me₃))₂ → Me₅C₅GeCH(Si(Me₃))₂ :Me₅C₅GeCH(Si(Me₃))₂ + LiC(Si(Me₃))₃ → (SiMe₃)₃CGeCH(Si(Me₃))₂ Stable also require bulky ligands: :Ge (SiMe₃)₂sub>2 + 2 LiC₅H₃(C₁₀H₇)₂ → Ge iC₅H₃(C₁₀H₇)₂sub>2 The C-M-C

bond angle Molecular geometry is the three-dimensional arrangement of the atoms that constitute a molecule. It includes the general shape of the molecule as well as bond lengths, bond angles, torsional angles and any other geometrical parameters that deter ...

in metallylenes is less than 120° confirming hybridization other than sp². The higher p-character for the C-M^II bond compared to the C-M^IV bond is reflected in its slightly higher

bond length In molecular geometry, bond length or bond distance is defined as the average distance between Atomic nucleus, nuclei of two chemical bond, bonded atoms in a molecule. It is a Transferability (chemistry), transferable property of a bond between at ...

N-heterocyclic silylene An ''N''-Heterocyclic silylene (NHSi) is a neutral Heterocyclic compound, heterocyclic Chemical compounds, chemical compound consisting of a Silylene, divalent silicon atom bonded to two nitrogen atoms. The isolation of the first stable NHSi, als ...

s are known to be stable for months and have been studied extensively.

Group 15 carbene analogs

In the group 15 elements the neutral

carbene analog (RN) is called a

nitrene In chemistry, a nitrene or imene () is the nitrogen analogue of a carbene. The nitrogen atom is uncharged and valence (chemistry)#monovalent, monovalent, so it has only 6 electrons in its valence level—two covalent bonded and four non-bonded e ...

. The

analog is a phosphinidene. There are charged group 15 carbene analogs as well, most notably phosphenium ions (R₂P⁺) which are isolobal with (hetero-)carbenes possessing a singlet ground state.

Group 16 carbene analogs

Carbene analogs of

group 16 element The chalcogens (ore forming) ( ) are the chemical elements in group (periodic table), group 16 of the periodic table. This group is also known as the oxygen family. Group 16 consists of the elements oxygen (O), sulfur (S), selenium (Se), tellur ...

s have been first reported in 2009.''Reactive Dications Tamed Main-Group Chemistry: Stabilizing positive charge with three nitrogen atoms yields stable group 16 complexes'' Steve Ritter

Chemical & Engineering News ''Chemical & Engineering News'' (''C&EN'') is a weekly news magazine published by the American Chemical Society (ACS), providing professional and technical news and analysis in the fields of chemistry and chemical engineering.Link
/ref>

Sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...

selenium Selenium is a chemical element; it has symbol (chemistry), symbol Se and atomic number 34. It has various physical appearances, including a brick-red powder, a vitreous black solid, and a grey metallic-looking form. It seldom occurs in this elem ...

and

tellurium Tellurium is a chemical element; it has symbol Te and atomic number 52. It is a brittle, mildly toxic, rare, silver-white metalloid. Tellurium is chemically related to selenium and sulfur, all three of which are chalcogens. It is occasionally fou ...

dication A dication is any cation, of general formula X2+, formed by the removal of two electrons from a neutral species. Diatomic dications corresponding to stable neutral species (e.g. formed by removal of two electrons from H2) often decay quickly int ...

s have been found to be stabilized by the diiminopyridine ligand DIMPY. For example, the reaction product of

triflate In organic chemistry, triflate (Preferred IUPAC name, systematic name: trifluoromethanesulfonate), is a functional group with the Chemical formula, formula and Chemical structure, structure . The triflate group is often represented by , as opp ...

S(Otf)₂ and (2,6-diisopropylphenyl)₂DIMPY at -78 °C results in an air-stable dicationic sulfur compound with a naked S²⁺ atom coordinated by three nitrogen atoms by dative bonds. : Dicationic sulfur Martin 2009

References

{{Reflist Octet-deficient functional groups Carbenes