A Synthetic Approach to Cross-Conjugated Organometallic Complexes Based on geminal-Diethynylethene and Co^III(cyclam)

Abstract

A series of CoIII(cyclam) complexes ([1a,b]­Cl, [2a–c]­PF6, [3]­Cl2, [4a]­(OTf)4, [4b]­(PF6)2, and [5]­Cl2) (cyclam = 1,4,8,11-tetraazacycloctetradecane) bearing a geminal-diethynylethene ligand (gem-DEE) is reported. Syntheses of these acyclic cross-conjugated complexes were accomplished in satisfactory yields, and structural characterizations established that the geometrical feature of gem-DEE is largely preserved upon metalation. Combined structural and electrochemical studies suggest that the gem-DEE ligand, as a σ-donor, is weaker than phenylethynyl but stronger than butadiynyl in CoIII(cyclam) complexes. Voltammetric analysis indicated a weak but discernible Co–Co coupling across the gem-DEE bridge in [3]­Cl2 and [4a]­(OTf)4, while the addition of a second acetylide in the trans position diminished such coupling in [4b]­(PF6)2. DFT analysis revealed significant dπ–π mixing around the cobalt centers with extended π-overlap in the highest occupied orbitals and substantial σ-based mixing in the lowest unoccupied orbitals of [3]­Cl2 and [4a]­(OTf)4, the latter of which likely contributes to the weak Co–Co coupling.

Redox Properties of Ferrocenyl Ene-diynyl-Bridged Cp*(dppe)M–C≡C–1,4-(C6H4) Complexes

“…The energies of the key molecular vibrations were computed for 1 n+ and 2 n+ (n = 0-2) to provide a point of reference between the experimental observations and the computational results. For the neutral complexes 1 and 2, the ν M-C≡C and ν C≡C vibrational frequencies are computed at 2047 cm -1 (1779 km/mol) and 2183 cm -1 (129 km/mol) (1) and at 2057 cm -1 (2028 km/mol) and 2184 cm -1 (138 km/mol) (2) in excellent agreement with the experimentally determined values ( Table 2). The vinyl ν C=C bands are calculated at 1472 cm -1 (291 km/mol) and 1590 cm -1 (278 km/mol) for 1, and 1472 cm -1 (304 km/mol) and 1590 cm -1 (314 km/mol) for 2.…”

Crystal structures of 5,12-dimethyl-1,4,8,11-tetraazacyclotetradecane cobalt(III) mono-phenylacetylide and bis-phenylacetylide

“…Interesting examples include magnetic couplings between Cr(cyclam) species mediated by ethynyltetrathiafulvalene ligands (Nishijo et al, 2011), formation of Co III (cyclam) dimers and trimers through 1,4-diethynylbenzene and 1,3,5-triethynylbenzene bridges, respectively (Hoffert et al, 2012), and phosphorescence from [Cr(cyclam')(C 2 R) 2 ] type complexes with cyclam' as either 5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (HMC;Tyler et al, 2016) or 5,12-dimethyl-1,4,8,11-tetraazacyclotetradecane (DMC;Judkins et al, 2017). A number of Co III -containing species have been elaborated in our laboratories, including the series [Co(cyclam)Cl] 2 (m-C 2m ) (m = 2 -6; Cook et al, 2015Cook et al, , 2016, the species containing cross-conjugated gem-DEE ligands ISSN 2056-9890 (Natoli et al, 2015(Natoli et al, , 2016, and the unsymmetric trans-[Co(cyclam)(C 2 Ar)(C 2 Ar')] type complexes (Banziger et al, 2015). Described in this contribution are the structural characterization of [Co III (DMC)(C 2 Ph)Cl]Cl (1) and [Co III (DMC)(C 2 Ph) 2 ]OTf (2), which were prepared from [Co III (DMC)Cl 2 ]Cl under weak-base conditions.…”

Crystal structures of two (5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane)iron(III) complexes

“…There has been recent interest in developing conjugated materials based on alkynyl complexes of 3d metals with cyclam (1,4,8,11-tetraazacyclotetradecane) or its C-functionalized derivatives as the supporting ligand (Ren, 2016). Noteworthy examples include magnetic coupling between Cr(cyclam) species mediated by ethynyltetrathiafulvalene ligands (Nishijo et al, 2011), the formation of [Co(cyclam)-Cl] 2 (-C 2m ) (m = 2-6) series (Cook et al, 2015(Cook et al, , 2016 and Cobased cross-conjugated gem-DEE complexes (gem-DEE is gem-diethynylethene; Natoli et al, 2015Natoli et al, , 2016Natoli et al, , 2019, and phosphorescence from [Cr(cyclam 0 )(C 2 R) 2 ]-type complexes, with cyclam 0 as either 5,5,7,12,12,14-hexamethyl-1,4,8,11tetraazacyclotetradecane (HMC;Tyler et al, 2016) or 5,12dimethyl-1,4,8,11-tetraazacyclotetradecane (DMC;Judkins et al, 2017). In particular, several trans-[Fe(cyclam)(C 2 R) 2 ]-type complexes were prepared by the reactions between LiC 2 R and [FeCl 2 (cyclam)]Cl (Cao et al, 2012(Cao et al, , 2013.…”