SYNTHESIS, STRUCTURE, AND REACTIVITY OF A STANNA(II)-NICKELA(II)-CYCLOBUTENE COMPLEX

The (ethyne)nickel(0) complex (iPr2PC2H4PiPr2)Ni(C2II2) (1) reacts with the stannene Sn[CH(SiMe3)2]2 below - 30-degrees-C to yield the stanna(II)-nickela(II)-cyclobutene complex (iPr2PC2H4PiPr2) activated NiCH = CHSn[CH(SiMe3)2]2 (2; 83%) as the kinetically controlled product; 2 has been characterized by IR and NMR spectroscopy and an X-ray crystal-structure determination. The latter shows the central four-membered ring to be planar with a long Ni-Sn bond [2.626(1) angstrom]. According to the temperature-dependent. NMR spectra, 2 dissociates reversibly in solution to the starting components. The synthesis reaction thus represents an equilibrium as long as the temperature is below 20-degrees-C. These observations indicate that the structural lability of the stanna(II)-nickela(II)-cyclobutene moiety is associated with the weakness of the Ni-Sn bond. The bonding situation in 2 is best described as an "inner complex" in which a stannyl anion is coordinated to a nickel(II) cation. An ethereal solution of 2 undergoes an oxidative addition of one ethyne C-H bond to the stannene at 20-degrees-C to give the Ni(0)/Sn(IV) complex (iPr2PC2H4PiPr2)Ni{eta(2)-HC = CSn(H)[CH(SiMe3)2]2} (3) as the thermodynamically controlled product. Reaction of 3 with CO liberates the new alkyne ligand.