The introduction of a heteroatom at the alkylidene carbon atom of calixarene complexes such as 1 results in an organometallic compound that shows properties of both Fischer carbenes and Schrock alkylidenes. Such modified alkylidenes allow access to dimetallic alkylidene complexes. For example, 1 reacts with [CuCOCl] to provide 2.

This report deals with the chemistry of anionic W-alkylidynes generated over the oxo surface defined by a calix[4]arene tetraanion. The exhaustive alkylation of [cis-(Cl)2W{p-But-calix[4]−(O)4}] (1), with an excess of alkylating agent led to [{p-But-calix[4]−(O)4}W⋮C−R][M] (R = Ph, M = 1/2 Mg, 2; R = Prn, M = Li, 3; R = SiMe3, M = Li, 4). The protonation [PyHCl] of 2 and 3 led to the corresponding alkylidenes [{p-But-calix[4]−(O)4}WC(H)R] (R = Ph, 7; R = Prn, 8), which were reversibly deprotonated back to the starting akylidynes using LiBu. The reaction of 2−4 with AgNO3 led to dimetallic alkylidenes [{p-But-calix[4]−(O)4}WC(R)Ag)] (R = Ph, 12; R = Prn, 13; R = SiMe3, 14). The alkylation of 3 and 4 with MeOTf occurred at the carbon in 4 and at both carbon and oxygen in 3 leading to [{p-But-calix[4]−(O)4}WC(Me)SiMe3] (9) and to a mixture of [{p-But-calix[4]−(O)4}WC(Me)Prn], (10) and [{p-But-calix[4]−(O)3(OMe)}W⋮C−Prn] (11), respectively. The functionalization of the anionic alkylidynes was achieved by reacting 2 with electrophiles such as PhCHO leading to [{{p-But-calix[4]−(O)4}WC(Ph)-C(H)(Ph)-O}2Mg(thf)] (15) and with Ph2CCO forming [{{p-But-calix[4]−(O)4}WC(Ph)-C(CPh2)-O}2Mg] (16). An indirect, but synthetically quite versatile, functionalization is the oxidation of 2 with I2 producing [{p-But-calix[4]−(O)4}WC(Ph)-I] (20). The alkylidenes 7 and 8 were unexpectedly unreactive in the presence of olefins and aldehydes, e.g., PhCHO, which formed a reversible adduct binding inside the calix[4]arene cavity. However, the trans labilization of the alkylidene functionality was achieved by reacting 7 with ButNC, a reaction leading to cis-stilbene and the WW dimer [{μ-p-But-calix[4]−(O)4}2W2(CNBut)2] (18). The one-electron oxidation of 2 by Cp2FeBPh4 followed two different pathways via the common free-radical intermediate [{p-But-calix[4]−(O)4}WC·(Ph)], leading to either 7 (hydrogen abstraction) or [{p-But-calix[4]−(O)4}2W2(μ2-η2:η2-Ph2C2)], (19). The nature of the anionic alkylidynes, the reaction pathways with electrophiles, and the one-electron oxidation reactions were analyzed using extended Hückel calculations.

The introduction of a heteroatom at the alkylidene carbon atom of calixarene complexes such as 1 results in an organometallic compound that shows properties of both Fischer carbenes and Schrock alkylidenes. Such modified alkylidenes allow access to dimetallic alkylidene complexes. For example, 1 reacts with [CuCOCl] to provide 2.

The chemically reversible reduction of [(Me) W(calix)] to the diamagnetic [(Me) W(calix)Na ] [Eq. (1)], without major changes in the connectivity of the molecule, illustrates the flexibility of the calixarene ligand and stresses its potential as a molecular functional model of heterogeneous oxo surfaces.