N‐Heterocyclic Carbene Stabilized Dicarbondiphosphides: Strong Neutral Four‐Membered Heterocyclic 6π‐Electron Donors

Abstract

In contrast to cyclic π‐conjugated hydrocarbons, the coordination chemistry of inorganic heterocycles is less developed. Dicarbondiphosphides stabilized by N‐heterocyclic carbenes (NHCs) NHC→C2P2←NHC (1 a,b) (NHC=IPr or SIPr) contain a four‐membered C2P2 ring with an aromatic 6π‐electron configuration. These heterocycles coordinate to a variety of complex fragments with metals from groups 6, 9, and 10, namely [M0(CO)3] (M=Cr, Mo), [CoI(CO)2]+, or [NiIIBr2], through an η4‐coordination mode, leading to complexes 2 a,b, 3 a,b, 5 a,b, and 6 a,b, respectively. These complexes were characterized by X‐ray diffraction methods using single crystals, IR spectroscopy, and DFT calculations. In combination these methods indicate that 1 a,b behave as exceptionally strong 6π‐electron donors.

Insertion of Ruthenium into an inorganic, cyclic biradicaloid

“…[7] The non-Kekulé molecule B with a central P 2 N 2 heterocycle, which is best described as a biradicaloid, has been intensively investigated in the last decade. [8][9] The addition to small molecules" [9][10] radical reactivity, [11] complexation of metal fragments, [12][13][14] and ring expansion by insertion of an organic moiety has been reported. [15] In the reaction with carbon monoxide or isonitriles, the expansion of the four-membered to a five-membered ring such as C is achieved by insertion of the carbon atom (Scheme 1).…”