Novel Ni(0)-COT Complexes, Displaying Semiaromatic Planar COT Ligands with Alternating C−C and CC Bonds

Abstract

Reaction of (R2PC2H4PR2)Ni(C2H4) with COT gives the mononuclear complexes (R2PC2H4PR2)Ni(η2-C8H8) (R = iPr 1a, tBu 1b). The COT ligand in 1a,b is planar with alternating C−C and CC bonds, corresponding to a formal semiaromatic [C8H8]- ligand. Reactions of 1a with (iPr2PC2H4PiPr2)Ni(η2,η2-C6H10) and of 1b with stoichiometric amounts of {(tBu2PC2H4PtBu2)Ni}2(μ-C6H6) or lithium afford the dinuclear complexes {(iPr2PC2H4PiPr2)Ni}2{μ-η4(1,2,5,6):η4(3,4,7,8)-C8H8} (2a) and {(tBu2PC2H4PtBu2)Ni}2(μ-η2:η2-C8H8) (2b; two isomers). The COT ligand in 2a is tub-shaped and olefinic, whereas in 2b (as in 1a,b) it is planar and semiaromatic. The products are characterized by IR, solution and solid-state NMR spectroscopy, and by X-ray structure analysis.