Dimerisation of Dipiperidinoacetylene: Convenient Access to Tetraamino‐1,3‐Cyclobutadiene and Tetraamino‐1,2‐Cyclobutadiene Metal Complexes

Abstract

The reaction of 1,2‐dipiperidinoacetylene (1) with 0.5 equivalents of SnCl2 or GeCl2⋅dioxane afforded the 1,2,3,4‐tetrapiperidino‐1,3‐cyclobutadiene tin and germanium dichloride complexes 2 a and 2 b, respectively. A competing redox reaction was observed with excess amounts of SnCl2, which produced a tetrapiperidinocyclobutadiene dication with two trichlorostannate(II) counterions. Heating neat 1 to 110 °C for 16 h cleanly produced the dimer 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne (3); its reaction with stoichiometric amounts of SnCl2 or GeCl2⋅dioxane furnished the 1,3,4,4‐tetrapiperidino‐1,2‐cyclobutadiene tin and germanium dichloride complexes 4 a and 4 b, respectively. Transition‐metal complexes containing this novel four‐membered cyclic bent allene (CBA) ligand were prepared by reaction of 3 with [(tht)AuCl], [RhCl(CO)2]2, and [(Me3N)W(CO)5] to form [(CBA)AuCl] (5), [(CBA)RhCl(CO)2] (6), and [(CBA)W(CO)5] (7). The molecular structures of all compounds 2–7 were determined by X‐ray diffraction analyses, and density functional theory (DFT) calculations were carried out to rationalise the formation of 3 and 4 a.

Tetraaminocyclopentadienone Iron Complexes as Hydrogenation Catalysts

“…DAAs have received renewed interest in recent years since our group has introduced a more convenient route for the preparation of DAAs such as 1a – 1c , which bear cyclic piperidinyl-type amino substituents (Figure ). The coordination chemistry of these alkynes, predominantly 1a , toward transition-metal − and main group elements − has been studied, with their reactivity often being distinctly different from that of conventional alkynes because of their latent diamino–dicarbene nature . Since the presence of amino substitutions appears to be favorable for the catalytic performance of CPD iron complexes as already demonstrated for diamino systems such as III , ,,, we envisaged that the preparation of symmetric as well as asymmetric tetraaminocyclopentadienone complexes related to IV from the DAAs 1a – 1c might give access to highly active hydrogenation (pre-)­catalysts (see box in Figure ), and our results are described below.…”

A boron, nitrogen-containing heterocyclic carbene (BNC) as a redox active ligand: synthesis and characterization of a lithium BNC-aurate complex

“…This is significantly more up-field shifted than those observed in most carbene gold( i ) complexes, but falls in the range expected for transition metal carbone complexes. 51 Single crystal X-ray analysis performed on the orange crystals of 5a revealed a lithium aurate complex (Fig. 4c).…”

Carbones and Carbon Atom as Ligands in Transition Metal Complexes

“…The free CBA 6b could not be obtained, but only the cationic 6bH + and 6bH 2 2+ are known and used as starting compounds for the syntheses of the related transition metal complexes [80].…”

“…The cod ligand can be replaced by bubbling CO through solutions of 6a-MCl(cod) to produce the related 6a-MCl(CO) 2 compounds (see Scheme 14) [79]. Transition metal complexes with 6b as ligand were obtained by reacting 1,1,2,4-tetrapiperidino-1-buten-3-yne with (a) [(tht)AuCl], (b) [RhCl(CO)2]2, and (c) [(NMe3)W(CO)5] during the reaction rearrangement of the starting buten-3-yne to 6b has occurred [80].…”

“…Stephan described the first carbodicarbene stabilized by flanking cyclopropylidenes, named carbodicyclopropylidene 7 (see Figure 9) [81]. Transition metal complexes with 6b as ligand were obtained by reacting 1,1,2,4-tetrapiperidino-1 -buten-3-yne with (a) [(tht)AuCl], (b) [RhCl(CO) 2 ] 2 , and (c) [(NMe 3 )W(CO) 5 ] during the reaction rearrangement of the starting buten-3-yne to 6b has occurred [80].…”