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

作者：Natoli Sean N; Azbell Tyler J; Fanwick Phillip E; Zeller Matthias; Ren Tong^*

来源：Organometallics, 2016, 35(20): 3594-3603.

DOI：10.1021/acs.organomet.6b00657

A series of Co-III(cyclam) complexes ([1a,b]Cl, [2a-c]PF6, [3]Cl-2, [4a](OTf)(4), [4b](PF6)(2), and [5]Cl-2) (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 sigma-donor, is weaker than phenylethynyl but stronger than butadiynyl in Co-III(cyclam) complexes. Voltammetric analysis indicated a weak but discernible Co-Co coupling across the gem-DEE bridge in [3]Cl-2 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 d pi-pi mixing around the cobalt centers with extended pi-overlap in the highest occupied orbitals and substantial sigma-based mixing in the lowest unoccupied orbitals of [3]Cl-2 and [4a](OTf)(4), the latter of which likely contributes to the weak Co-Co coupling.

• 出版日期2016-10-24