Ruthenium carbenes, famously used in olefin metathesis, have impacted numerous research areas, ranging from synthesis to materials and biology. Although in the same group as ruthenium, iron carbenes showing similar reaction patterns have not been reported. Such targets are of high interest because the use of a sustainable metal would lead to a decreased cost, toxicity, and environmental impact of the corresponding compounds. Herein, we report the synthesis of an iron carbene complex, [{PC­(sp2)­P}­Fe­(N2)­(PMe3)] ([PC­(sp2)­P] = (bis­[2-(di-isopropyl­phosphino)­phenyl]­methylene), which is capable of performing [2+2] cycloaddition reactions in the presence of alkynes. Specifically, η3-vinyl carbenes are formed stoichiometrically through a [2+2] cycloaddition between the alkyne and the metal carbene. Additional reactivity of the η3-vinyl carbenes with alkynes yields a second insertion product containing a new iron carbene moiety.

Unprecedented sequential substitution/reduction synthetic strategy on the Pd radical carbenes afforded heterobimetallic Pd–K carbene complexes, which features novel Pd–Ccarbene–K structural moieties.

A series of palladium pincer complexes supported by ( i Pr2P-C6H4)2CH2 (PC­(sp3)­H2P = bis­(2-(diisopropylphosphanyl)­phenyl)­methane) was isolated and characterized. Different modes of C–H activation were observed for [{PC­(sp3)­H2P}­PdX2] (X = Cl, OTf, Me, OAc). The thermal treatment of [{PC­(sp3)­H2P}­PdX2] (X = Cl, OTf) induced a backbone C–H bond activation to generate the respective [{PC­(sp3)­HP}­PdX] complex, while under similar reaction conditions [{PC­(sp3)­H2P}­PdMe2] underwent a C–C reductive elimination that led to the formation of a Pd(0) dimer, [{PC­(sp3)­H2P}­Pd]2. For the analogous diacetate complex [{PC­(sp3)­H2P}­Pd­(OAc)2], the C–H activation occurred at the phosphine isopropyl methine group to generate a palladacycle.

A square planar platinum­(II) carbene complex [{PC­(sp2)­P}H­Pt­(PMe3)] ([PC­(sp2)­P]H = (bis­[2-(di-iso-propyl­phos­phino)­phenyl]­meth­ylene) was synthesized through the dehydrohalogenation of [{PC­(sp3)­HP}H­PtCl] in a microwave reactor. The tert-butyl substituted analogue, [{PC­(sp2)­P} tBu­Pt­(PMe3)] ([PC­(sp2)­P] tBu = bis­[2-(di-iso-propyl­phos­phino)-4-tert-butyl­phenyl]­meth­ylene), was synthesized via an analogous route. The nucleophilic nature of the carbene carbon was confirmed through DFT calculations and reactivity with HCl. Additionally, [{PC­(sp2)­P}H­Pt­(PMe3)] was treated with 0.5 equiv of I2 to generate a paramagnetic product, [{PC­(sp2)­P}H­PtI]. The Evans method and EPR spectroscopy revealed that a one-electron oxidation occurred at the carbene carbon, thus generating a persistent radical carbene.

A series of mono and bi-radical carbenes.

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